Chest (singular) refers to the whole of the front of the torso - from the throat to the abdomen. Men, women and children all have chests. When we talk about chests we are often referring to our lungs and respiratory systems - for example 'My grandpa worked in a mine so he now has chest problems.' Breasts and boobs (plural for obvious reasons!) are what women have. 'Breasts' is a neutral anatomical term. 'Boobs' is informal - a bit rude, funny or cheeky, depending on context. Someone might say 'breasts' when talking to a doctor, and 'boobs' when talking to friends. We also have the rather old-fashioned and literary word 'breast' (singular), which is the equivalent of 'chest'. For example, you might come across a poem referring to hearts beating in someone's breast, but the word is rarely used in this sense in modern-day English.