The brand name "Pyrex" was originally for borosilicate glass, which was sold by Corning to the laboratory market for chemical glassware and the consumer market for cookware. Borosilicate was developed around 1893 by Schott as a low expansion co-efficient glass material.
Corning 7740 and Schott 8330 are current borosilicate products (with the same nominal composition) for technical uses.
Corning exited the consumer market in 1998, spinning it off as "Corelle".
Since then, other companies have licensed the trademark "Pyrex" or "pyrex", and some use it only for non-borosilicate tempered soda-lime glass cookware, which is probably cheaper.
There are many claims that the non-borosilicate "pyrices" are more susceptible to thermal shock (see
https://en.wikipedia.org/wiki/Pyrex )
(H.L. Mencken claimed that the etymology of the trademark was not from the Greek for "fire", but due to an early product being a pie plate; I am dubious.)