With Dyes the terms Crocking and Bleeding are often used interchangeably. There is however a slight difference in meaning which can be subtle.
Crocking refers to when excess dye or improperly fixed dyes leaves the primary textile and attaches itself to another surface. Crocking is most commonly used to refer to dry dye transmittal usually by rubbing. However Dyes can crock wet or dry. When dyes crock in solution it is often referred to as bleeding so in some cases bleeding and crocking can describe the exact same condition.
Bleeding can also refer to other conditions. Crocking specifically covers excess or improperly fixed dyes. So when the dye was properly fixed and then damaged “Bleeding” is used to describe this condition. In a recent survey of the technical literature all usages of “Bleeding” that I saw referred to wet dye transmittal. So take for example a rug whose wool is properly dyed with an Acid Dye. Then as is common with Oriental Rugs the dyes can be damaged and their fix to the wool can be broken. Two common ways this happens is by washing with a highly alkaline cleaning solution or by soaking a rug in Urine. Since industry sources estimate that 80% of wool rugs washed by professionals involves pet accidents urine contamination is a serious issue. The two are similar because the urine turns alkaline and can cause dye instability in much the same way as an alkaline detergent. Of course many factors come into play so what I can safely say is that high alkalinity increases the odds of dye instability in wool rugs.
So when dye is transmitted by dry rubbing it is crocking but when the dye transmittal is wet it may or may not be crocking but it is bleeding.