Ulceration is the noun. It covers two closely joined things, and English lets it swing between them. First, the process: the tissue breaking down and opening into sores — 'ulceration of the stomach lining took several weeks'. Second, the result you can actually see: the sores themselves, taken together — 'there was ulceration across the whole area'. That second use is why doctors can say 'extensive ulceration' where you might expect 'many ulcers'. Notice that in this second use it behaves as an uncountable noun: you say 'some ulceration', not 'an ulceration' or 'three ulcerations'. (You will occasionally see a plural in older medical writing meaning individual sores, but modern usage avoids it.) This is a formal medical word — it belongs to reports, textbooks and doctors talking to each other. A patient would say 'I've got ulcers' or 'it's gone all open and raw'; the notes would say 'ulceration'. If you must choose one word from this family to know, know 'ulcer'; ulceration is what you read, not what you say.

潰瘍、潰瘍形成（名詞）。指潰瘍發生的過程，也指看到的潰瘍面。台灣病歷、醫學報告常見「潰瘍形成」「廣泛潰瘍」。