What's the term for these type of 'riddles'?

[Meg]

For example:
MIND
_____
MATTER

Would be "Mind over Matter"

Another would be (imagine it this way) the word "walk" written sideways, down to up. The answer would be "sidewalk"

I know it's a little confusing, so if you need anymore, I can give 'em. Thank in advance!
Thanks for the help Penney. And the "BACK" one was funny =)

 

[Zezima]

These are called word scrabbles........................................................................................................................................................................................................as i call them..................

 

[Penney]

They are called REBUS puzzles.
Have a look at:
http://www.fun-with-words.com/rebus_puzzles.html

I love them!

 

[C_T_W]

I'd give penny the 10 points here.

my favorite.

BACK
BA
B