Does this mean "they lost a lot... of things", or as in "they lost a lot... of times"?
Hum.... another sentence that we have to guess the meaning. Theres no context,so it might be many things. "eles perderam muito... dinheiro (money), tempo (time)..." you have to use singular/male words (cuz of the word 'muito'). But, for instance, some friends havent gone with you on a trip, and now you're telling someone how much they've missed, then you can say "eles perderam muito....", that is, they would have the opportunity to see and do many things if they had gone...