Boot worship is a term for the practice of extreme adulation of boots in BDSM.
It is related to foot worship in a derivative way, in that the adulation may really be attributable to the proximity of the boots to their owner. If the foot is usually considered one of the "lowest" and least appreciated parts of the body, the "sub"'s reverence for the footwear that encloses her or his dom's foot is a concrete admission of inferiority.
Thus boot worship may include sniffing or inhaling from worn boots, as well as licking, kissing or cleaning their exteriors. It may also consist, more passively, of the woman or man lying prone and being "trampled" by her or his dom. Heeled boots may lend themselves to sucking, in an approximation of fellatio.