'Wolds' means an area of open, rolling hills with few trees — gentle high ground, not sharp mountains. You will meet it mostly inside English place names: the Yorkshire Wolds, the Lincolnshire Wolds, the Cotswolds. That is the honest situation with this word: it is really a piece of British geography vocabulary, and outside Britain almost nobody uses it in ordinary talk. The singular 'wold' does exist and means one such stretch of hilly open country, but it feels old and poetic — the sort of word you meet in a nineteenth-century poem, not in conversation. When British people say 'the Wolds' with a capital letter, they usually mean one particular famous area near them, and everyone local knows which one. So treat this as a word to RECOGNISE, especially when reading about England or seeing it on a map, rather than a word you need to produce.