If something is electronic or digital, it means a computer can read it. In fact, only a computer can read it (easily, that is). It's information that has been binary-coded, reduced to 1's and 0's.

Resources that are electronic are often shortened to e- (e-journals, e-books). They might also be called digitized or digital, which means they're made into a format a computer can read.

The terms electronic and online are often used interchangeably, but this is not necessarily correct. A resource can be electronic but not available online. For instance, it could be on a CD-ROM and then you'd need to have the CD-ROM in your computer to use it. An online resource can be accessed over the internet.

Electronic or digital refers to the format of the item, whereas online refers to its location or accessibility.