In popular music, half time is a type of meter and tempo that alters the rhythmic feel by essentially doubling the tempo resolution or metric division. Thus 4/4 approximates 8/8. It is not to be confused with alla breve or odd time. Though notes usually get the same value relative to the tempo, the way the beats are divided is altered. While much music typically has a backbeat on quarter note (crotchet) beats two and four, half time would increase the interval between backbeats to double, thus making it hit on beats three and seven (counted out of an 8 beat measure [bar], common practice in half time):

1   2   3   4   1   2   3   4
1   2   3   4   5   6   7   8
1       2       3       4

Essentially, a half time 'groove' is one that expands one measure over the course of two.