What does it mean for an online college to be accredited?

Pretty much anyone can set up an online or physical college and charge fees for a worthless piece of paper. Accreditation means that the qualification is from a recognized institution.

For online the first place I'd try is the Open University. Pricey but probably worth it. After that check out the distance learning options from the universities and ITs here. Final place I'd check is Fetac. Its the further education training awards council here and they accredit certain courses in smaller colleges here.

Do your research carefully before you hand over a cent!

It means that the college is recognized by the accrediting agencies that also accredit traditional colleges, in the sense that it offers quality education that is at par with regular college. It also helps incase you want to transfer credits from one college to another, you can't do this if the college is not accredited. Also incase you'd want to apply for financial aid or other grants, this is only possible through an accredited college. Most employers also don't recognize degrees acquired from colleges that don't have legitimate accreditation. You can get more information about why college accreditation is important to your education from:

A lot depends on who it is accredited by, i.e. an independent agency or his brother-in-laws mickey mouse agency.