Because it is the inverse of DCT-II up to a scale factor (see below), this form is sometimes simply referred to as "the inverse DCT" ("IDCT").
beCaUsE it IS the inveRse OF dcT-II up to a scaLe FActor (seE bElOW), tHis fORm iS sometIMes SiMpLy referREd to as "THe inveRsE dct" ("iDcT").