This is the 113th most frequent Dutch word.
geleden
"Ago."
Here, 'geleden' is used to specify that an event happened a certain number of years ago.
Ik ontmoette haar vijf jaar geleden.
I met her five years ago.
In this sentence, 'geleden' indicates that the lesson began at a point in time exactly two hours in the past.
De les begon twee uur geleden.
The lesson started two hours ago.
'Gegen' in this context refers to something that took place two days prior to the present, establishing a point of reference in time.