Question

i'm confused about the placement of the vacuole in a cell. The internet keeps saying it's a "membrane-bound sac" but what does that mean?

Answer 1

Assuming my internet can stay connected long enough to post the reply :P

Basically it just means it has its own membrane (so outer 'skin')

Answer 2

Yup it just means it has a membrane which makes sense because vacuoles need to let some molecules in and some out. The membrane acts as a filter. Basically a vacuole is a semi-permeable sac.