It's called lots of things... alt tags, span tags, hover text, mouseover text...

Whatever your preference, it 'aint working right in the customer CP.

Specific to Internet Explorer (does not appear to be a problem in Firefox), in the customer CP - features tab, when you hover over the blue question marks, the hover text reads "Specify your local timezone here."

This same issue also appears in...
Features - Call Routes
Features - Tele Block
Voicemail (all hover text)
Preferences (only the Change Password question mark has incorrect hover text)

As a sidenote, again specific to IE, the font in the Features - Devices section is extremely small, and should probably be bumped a few points to be readable.