It is a tool, launched in 1975 by the ISI, for ranking academic journals analysing citations count, journal impact factor and journal immediacy index. Presently it has two annual editions for science and social sciences, based on SCI-E and SSCI.

It is the average number of times that an article published in a specific year within a specific journal is cited over the course of that same year.

It is the number of current citations to articles published in a specific journal in a two year period divided by the total number of articles published in the same journal in the corresponding two year period.