E-resources

It's a computer program - normally rather short and with the possibility to interact with it - giving you information about some specific subject or topic.

Short form for online public acces catalogue, it is an online database of  bibliographic materials held by a library.

It is used to locate books and other material available at that library.

used for digital resources available without fee in Internet or in an institutional repository.

in: "on the Internet" - consider it idiomatic.

The term "open access" was first used in the late 1990s and early 2000s, when the open access movement was established, and then it was officialized through 3 worldwide initiatives: the Budapest Open Access Initiative (2002), the Bethesda Statement on Open Access Publishing (2003), and the Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities (2003).
The open-access movement strive to provide free online access to scientific literature, primarily intended for scholarly journal articles, but also for thesis and ebooks.
The publishers generally own the rights to the articles in their journals. Anyone who wants to read the articles must pay to access them. Anyone who wants to use the articles in any way must obtain permission from the publisher and is often required to pay an additional fee.
Although many researchers can access the journals they need via their institution and they may think that the access is free, but in reality it is not so. The institution has often been involved in lengthy negotiations around the price of their license.
Authors can provide open access in two ways: by self-archiving their journal articles in an open access repository, or by publishing in an open access journal.