1. Noun, used as a suffix

   not exceeding ...; not more than ...; ... and under; ... and below; ... or fewer

   １６歳以下の子供は劇場には入場できません。

2. below (a standard, level, etc.); under; beneath; less than

3. Noun, Noun which may take the genitive case particle 'no'

   the following; the below-mentioned; the rest; followed by ...

4. Noun, used as a suffix

   including ...; ... and other (employees, officials, etc.)

   used to refer to all members of a group, starting with the head or principal figure

Also written 已下【いか】ika