My understanding and looking at the results at Gedmatch, generation 4 means a third cousin. So, for example I have my daughter and my results at Gedmatch and she is one generation away from me while a second cousin who also has her results on Gedmatch is shown as 3 generations.

Thus, four generations (a third cousin) means that your MRCA would be a great great grandparent.

Oh and the other thing about autosomal DNA is you don't get exactly the same amount of DNA from each generation so the number of generations won't be exact. So, for example I have two known second cousins over at Gedmatch (one whose paternal grandfather and my paternal grandfather are brothers and one whose maternal grandfather and my maternal grandfather are brothers). One is 2.7 generations from me and the other is 3.3. Clearly I have more DNA in common with the 2.7 generation second cousin than the 3.3 generation second cousin. That can easily happen.