This is the yellow strip on the top of an ink cartridge. It covers the air hole on the top to prevent evaporation and leakage before installation. Removing the seal release the vacuum and allows the ink to flow through to the print head.
Remove the seal carefully! Ripping it off could cause ink to spill out everywhere!
Slowly peel it back being carefull not to squeeze the cartridge sides when you are holding it.
If you need to re-seal an ink cartridge for use later on, re-install the protection cap if provided & wrap the whole cartridge tightly in cling film. Store upright in a dark place.
If the ink cartridge seal is not removed properly the printer may continue to print using up the residual ink in the head or carrier, it will then begin to suck air an you could damage your printhead!