“Tachiyomi” literally means “standing reading” and describes the practice of going to a bookshop and standing there reading the magazines or books.
In my native NZ, within 5 minutes of me entering a bookshop and opening up a magazine, a not so friendly shop assistant would inevitably pipe up with “are you going to buy that?”. In Japan however, there is a lot more acceptance of the practice – especially for magazines. Less so for manga though – you’ll usually find these sealed in plastic to prevent cheapos from reading the whole thing at the bookshop.
Some places might have a sign like ‘立ち読みをご遠慮ください。’ (please refrain from standing and reading) but this is very rarely enforced.
There are certain times in the year that can make your visit to Tokyo less than idea.