I still prefer "secrets" or "easter eggs" or "special items" as the primary descriptive term... but that's just my opinion.
Achievements are different than secrets or easter eggs. Some games tack have ridiculously easy achievements.... WHOA CRAP I JUST REACHED A HEAD SHOT COUNT OF 10!!! or NICE!!!11 I'VE COMPLETED LEVEL 1!!!!. bloodiblup<img src="http://www.xboxmodstore.com/360/XCLOSEUP.jpg">
100 GAMER SCORE
Back in the golden years easter eggs were SUPER secret and nearly impossible to find. Finding one by yourself was like a giant event that you talked about for days. Achievements are like: "heh sweet. continues shooting..."