A thrifty person is careful with money. They do not waste it, they compare prices, they mend a shirt instead of buying a new one, they cook at home instead of eating out. It is a compliment — you are saying the person is sensible and manages well, especially on a small income. Things can be thrifty too: 'a thrifty meal', 'thrifty tips for students' — meaning cheap in a clever way, not cheap in a sad way. Note how different this feels from 'cheap' used about a person, which is an insult ('Don't be so cheap'), or 'stingy' and 'mean', which say someone holds money back from others. Thrifty says the opposite: this person spends carefully so there is enough. Though actually, the word has an old-fashioned smell to younger speakers. It sounds like something you say about a grandmother, or something you read on a money-saving website. Younger people are more likely to say 'good with money', 'careful with money', or 'budget' as an adjective — 'budget travel', 'a budget meal'. It is still perfectly usable and everyone understands it; it just feels warm and slightly old. In American English there is also 'thrift store' — a shop selling second-hand clothes and things, run for charity — which keeps the word alive in daily life even for people who would never call anyone thrifty.