I see the word "Do" repeatedly after the father or Mother's name in baptism records from Ireland in 1878. What does this mean? It looks like it might mean ditto, but I'm not sure.
Yes, Do is an abbreviation for ditto.
It will help to see the batch - but you are probably correct that it likely means ditto. You can see the batch code at top of the web indexing view
project name [batch code]
Or Help> Share Batch.