what was "virtual representation"?

Answer 1

English principle stating that the members of parliament represented all of Britain and the British Empire, even though members were only elected by a small numbers of constituents
this idea was meant to be a response to the colonial claim of "no taxation without representation," meaning that parliament was itself a representation of those being taxed

Answer 2

it was a concept coined by the political writer Edmund Burke which stated that since everything that parliament did was aimed to benefit all Englishmen and since the American colonies were English they were virtually or the same as represented even though there were no representatives from the colonies.