When looking at a lead in Detail View, there are sub-panels that display Activities and History for that Lead. You can also Add Tasks for that Lead from the Activities block (see screenshot to supplement my poor explanation!)
By default the text ‘Create Task’ is displayed - I’d like to change that wording. I assume this has to be edited in a file - which file would that be?
First of all, have a look at the option Admin / System Settings / Display actions in menus. I always turn that off so that all buttons are immediately visible, both on the top of Detail views, and in subpanels. Saves users a LOT of clicks.
Then, the definitions you’re looking for are here: