A bar is something two guys usually turn into :0
Seriously, a bar is a logial subdivision of music, defined as n notes of m type (I hesistate to say duration here), where type is a 16th, 8th, quarter, half note, etc.
Typically in rock a bar is 4 beats in length, where the type is a quarter note.
Beyond that, this is pretty much music 101.
Now as to length of a song, no one gets paid by number of bars or the number of notes they write. Songs are usually 3 minutes or so in the modern format (someone correct me if this has changed). Used to be bands could get by with 10 minute works, but I guess the fear is that the attention span recent generations couldn't handle that...
jamesborn54 said:
hey guys whats a bar when writining a song how much do I write or what ever is ther a guide line or something