Undifferentiated describes something that has no clear separate parts, or that has parts you cannot tell apart from one another. It is the negative of "differentiated", so it always points at a difference that is missing. Two common ways it works: (1) a mass or group that has never been split up — an undifferentiated crowd, an undifferentiated block of time, an undifferentiated grey sky, where nothing stands out from anything else; (2) things that are technically separate but look or feel the same, so you cannot sort them — "the shops all sell the same undifferentiated products", meaning nothing makes one different from another. In biology it has a precise use: an undifferentiated cell is a young cell that has not yet become a particular kind of cell (a muscle cell, a nerve cell). Stem cells are undifferentiated. In business writing it is nearly an insult — an undifferentiated product has nothing special, so people buy it only on price. The word is formal and long; you meet it in textbooks, science writing, and business reports far more than in speech. In everyday talk people just say "all the same" or "all mixed together". Note it describes a state, not a fault of the person looking — that is a different word (see "undiscriminating").