I was recently reading a paper in some journal which described part of their method in the following way:
Our goal is to perform [something] on our data, which is drawn from [distribution]. This poses a problem because [reason]. We therefore took inspiration from Author et al. (1970) and propose to augment our method by [description of the modifications, including equations]. There are two challenges in this case: [first challenge, including a citation] and [second challenge]. We solve these by [mathematical description, including equations].
I wanted to learn more and looked up the cited paper (from different authors). Unfortunately, there wasn't more to learn as it turns out that the description (about 2 paragraphs, including the brackets) was copied near verbatim. In the quote above, the italic part was obviously added, and the wording was slightly changed a few times (e.g. from "there exist many ways to ..." to "there are many ways to ..."), but most of it is completely identical.
IMHO, this is way above the threshold of plagiarism. But it is a good idea to do something about it (e.g., contact the journal, or politely tell the authors to get their scholarly act together if I happen to meet them at a poster session) or is it better to let it go?