1. counter for (small) things or pieces
also written as ヶ
次は、最低でも千個は集めてやるからな！Next time I'll collect at least a thousand, you'll see!
2. counter for military units
3. (an) individual; one person
今は集団より個を大切にする時代だ。These days, we live in an age that values the individual over the group.
4. counter for years (of age difference); counter for school-years
だって彼女は俺の七個下だよ？But she is seven years younger than me, you know?