Titles are in-game challenges unrelated to other achievements. There are 135 titles to be earned. You earn titles for doing just about anything, from walking, running, to headshots, weapon kills and completing chapters in campaign. You’ll earn far more than 10 titles by just playing through the game.
Once you’ve earned 10 different titles, choose Play Game -> Dog Tags from the main menu and the achievement will unlock there.
You can see a list of titles and their requirements, provided by X360A user BounTyHunteR Zero HERE.