Crossdressing (or sometimes known as transvestism) refers to the act of wearing clothes and other accoutrements commonly associated with the opposite sex within a particular society.
Sissy (derived from the sister word in English “sister”; also, baby ladybug, ladybug child, effeminate man, etc) is a pejorative term for men interested in traditionally feminine pastimes, which shows effeminate behavior, being little athletic.
The term Sissy is mainly from the BDSM culture, and it deals with forced feminization, the dominated person (men subjected to transvestism) are called Sissy as a form of erotic humiliation, which may provoke guilt or sexual arousal, or possibly both, depending on the person. Stereotyped “feminine” activities (for example, cleaning, putting on makeup) are usually assigned.
In particular, a very common theme is the “sissy maid” training. In a typical scenario, a submissive maid, dressed in a sexy maid uniform, often to increase sexual excitement. The activities they usually carry out range from routine housework that a real maid, to degrading tasks for erotic humiliation. They are also instructed to perform sexual acts, always in a submissive or passive role.