Confusion about TEFL

As the title says I'm just wondering what a "TEFL" certificate is. Is the TEFL a certificate on its own or does encompass all other certificates like the TESOL, CELTA and TOEFL. Which would be the best one to get if you plan on teaching English abroad, specifically Japan, but I'm not too sure whether or not that would hold any significance in what certificate I would pick.

A TEFL or TESOL certificate is the general name for such certificates. Some are reputable; some are not.

The two most widely known ones in the British area of Influence are Cambridge's CELTA and Trinity's Cert Tesol.