Tailoring has two closely linked meanings. First, it is the work or the trade of making clothes — especially men's suits, jackets and coats — cut and sewn to fit a person's body. "He learned tailoring from his father." "a tailoring business". Second, and this one surprises students, it means the cut and construction of a garment — how well it was made, how the shape sits on the body. Here you talk ABOUT a finished jacket: "The tailoring on this coat is beautiful." "Cheap tailoring shows at the shoulders." In this second use it is a quality word, common in fashion writing and in shops. There is also a fashion sense you will see in magazines: "tailoring" as a category of clothing means structured, suit-like clothes — blazers, trousers with a sharp line — as opposed to soft or casual clothes. "This season is all about tailoring." The word is uncountable: no "a tailoring", no "tailorings". Note that it is not the -ing form of a verb here in these uses; it is a noun in its own right. Separately, the verb "tailor" is very common in the figurative sense of adapting something to fit a need — "We tailored the lesson to the students' level" — and "tailoring" can be that verb's -ing form too: "tailoring the course to each group takes time."