Is tbody relatively new, because I never remember using it when I used tables a while back.
Well, possibly newer than <table>. I first remember seeing it in 1999, but I saw <table> in 1996. Dunno if it was there prior to that.
Modern browsers all automatically give you a <tbody>, even if you don't explicitly code one. But you can, indeed, explicitly code it. Just as you can also explicity code <thead> and <tfoot>.