That's easy; a lead is any role I play. 

Did you ever see "Shakespeare in Love"?  At a party, somebody asks the guy playing the nurse what this new play called Romeo and Juliet is about.  He says, "It's about this nurse . . . "

Seriously, it really depends on who is asking the question and why.  To a dramaturg, "lead" could be synonymous with "protaganist" or "antagonist."  To an actor, it's any role that will make his buddies say, "You were the only thing worth watching in that piece of junk."  To a director, it's the roles she needs to cast with actors who can actually learn lines and have some clue of how to act. 

Personally, I've never found the term useful.  Of course, I don't get cast as leads. 

P.S.  (just to contradict myself for a bit) You don't think McMurphy and Nurse Ratched are both leads in Cuckoo's Nest?  When I did the play about 12 years ago, we had every actor in the city out for one of those two roles.  Now THERE's a working definition of a lead!

Regarding Cuckoo's Nest, I don't think of Ratched as quite a "lead."  This doesn't mean that I think she's unimportant or anything, and, certainly, it's a role that I'd give my left arm for (if I were female).  But, to use my test, I think you can write a single-sentence summary of the plot without using her; McMurphy's action is more about trying to get his fellow inmates to stand up for themselves than in fighting her (although fighting her is HOW he gets them to stand up for themselves).  I see her more as "villain" than "lead."  Admittedly, a bit weaker case than saying Anarchist or Oedipus has a single lead.

I agree that Nick & Honey are supporting characters, but I don't know that there can't be shows with 4 leads AT ALL.  5 I can't seem to make work, though.

Title character as lead works sometimes, and, yes, Godot and Harvey could be considered leads (although I'd argue that since neither is real, they're more of concepts than characters- I mean, would you call the tape the lead in Krapp's Last Tape?).  But, to make an obvious exception to title-character-as-lead: The Rocky Horror Show.

To be or not to be, that is the question.

Whether 'tis nobler in the mind to suffer

The slings and arrows of outrageous fortune,

Or to wait until the morrow comes,

For shalt not the sun come up upon the morrow?

Verily, 'tis a hard-knock life for us,

'Stead 'a kisses, we get kicks anon.

To sleep, perchance to dream, aye, there's the rub,

But Easy Street is where one sleeps till noon.

Soft you now, the fair Sandy, nymph?

In thy horizons be all my sins remembered.

I hope that was funny, because I feel so . . . dirty.

Topper:

Unfortunately, the best musical version of "Hamlet"
was already performed by the castaways of
"Gilligan's Island."

Be not a borrower, nor a lender be!

I will probably never forget that episode.....

True.  However, this:

http://www.robinjohnson.f9.co.uk/adventure/hamlet.html - http://www.robinjohnson.f9.co.uk/adventure/hamlet.html

is the best version of Hamlet overall.

Well, I think there can be up to four leads. That is in a large enough show... A show with a large cast, such as The Crucible (where I think Giles Corey is a lead character. Hahaha...kidding...played the role, thought I'd get my jabs in), you can have

First Male Lead - The principal male character in the story. In the case of the Crucible, John Proctor.

First Female Lead - Again, principal female character in the story. Crucible's example is Abigail Williams

Second Male Lead - Harder to define, but in The Crucible, this would fall to Rev. Hale, since he has the greatest character development next to Proctor.

Second Female Lead - The most character-developed female role next to the First lead. The Crucible would be Elizabeth Proctor.'

It ultimately depends on the show and the interactions with the characters.

This is a great question.

I've noticed on some resumes that people are putting 'lad' beside their character's name - because they had a few lines.  arrgh

You have to go back to analyzing the script.  Most plays have 3 or 4 leads:  your protaganoist (your hero), your ingenue or juvenile (another protagonist type but one that is protect and rescued by the hero); the antagonist (villian--sometimes two).

Your supporting are the group that play side-kicks, etc.  Like Le Fou and Maurice in Beauty and the Beast.

Your minor roles are those with speaking roles that actually develop the characters well but don't spend enough time on stage to rate supporting status.

Your walk-ons/chorus help show the reaction of the common man (the audience member).  They generally have few lines individually and sing the reprises of the songs.  They may also sing entire ensemble numbers.  Some chorus ensemble numbers have lines that are specified for particular chorus members, but these members generally fall into another category anyway (Lumiere in B&B would be supporting where as his feather duster girlfriend would be considered either minor or chorus).

I think it is anyone who has between 20 and 40 post on the Community Theater Greenroom Message Boards.  Then you become a star.  Maybe Mike or Chris could chime in and give us the true definitions and breakdown.

In theater terms, the true definition would be the character that drive the plot.  Dracula is a lead although spends less time on stage then Van Helsing.  In Guys and Dolls, Sky and Sarah and Nathan and Adelaide are leads, while Nicely Nicely could be considered a lead, it is up to debate.

Want the true definition of a lead.  Ask EQUITY for their definition.  In Joseph, Contracts diminish rates as Joseph, Jacob, Narrator.  Jacob is on stage for 17 minutes. The Narrator usually never leaves.  I would assume equity would give you a true definition is terms of financial terms.

Nice!

Well, since falstaff29 had 22 post when he replied, maybe the magic number is 25

Isn't this a movie term more than a stage one?

Best Actress (Leading Role)

Best Actress (Supporting Role)

Personally I've never cast a Lead in my life, just an actor/ress!

I directed "Cuckoo's Nest" a few years back, and I considered the Chief to be the lead. It's his story. His is the character that grows and changes through the show. McMurphy is just the catalyst.

At least that's what I told the actor I was recruiting for the part.

I told the actor I was recruiting for Nurse Ratched that her's was the lead. Same with the actor I wanted to play Billy. So I guess the lead would be whichever character I'm recruiting for at the time.

But my real answer is that I don't believe in leads in theater. I try to create a team, a 'community' on stage where the contributions of all the actors are equal in importance, if not in line length. The actors who feel they have to be recognized as the lead, I call them divas, then don't usually ever cast them again.