Metrobús is a 10 trips ticket valid for both buses and subway. There's no "Metro" only ticket (well, except if you buy a single ticket).
I think in Barcelona you can buy a 10 trips ticket for Metro only but in Madrid there is only Metrobús which, in my opinion, is very convenient.
Regards,
Antonio
PS: My advice is always to check the official site. Here is the link:
http://www.metromadrid.es/red/billetes/main_i.html [This message has been edited by Antonio (edited 06-25-2000).]