What does ago mean?
The definition of ago
A*go”, a. & adv.
Etym: [OE. ago, agon, p. p. of agon to go away, pass by, AS. agan to pass away; a- (cf. Goth. us-, Ger. er-, orig. meaning out) + gan to go. See Go.]

Past; gone by; since; as, ten years ago; gone long ago.