"Slit" is an ambiguous term that can refer to many things. Please use a more specific tag if possible, such as:

Orifices

"Slit" is common slang for feral, scalie, amphibian, avian, etc orifices, particularly orifices with a completely retractable penis, subtle pussies, or ambiguously-gendered orifices.

• ambiguous_slit - a genital orifice on an ambiguously-gendered character. This orifice does not help identify the character's gender.
• anus
• horizontal_anus
• cloaca - contains the genitals and the rectal tract
• cloacal_rectum
• horizontal_cloaca
• vertical_cloaca
• genital_slit - contains only the penis
• mammary_slits - folds of skin that can enclose nipples
• pussy
• innie_pussy - only the external labia are visible. No visible clitoral hood, clitoris, or labia minora.

Other

• slit_pupils
• side_slit / side_slit_clothing
• slit_(wound)