- || -- a binary operator, often used for vertical concatenation

- "Expression | Expression" -- see Expression -- the class of all expressions
- "Expression | Holder" -- see Expression -- the class of all expressions
- "Expression | Thing" -- see Expression -- the class of all expressions
- "Holder | Expression" -- see Expression -- the class of all expressions
- "Holder | Holder" -- see Expression -- the class of all expressions
- "Thing | Expression" -- see Expression -- the class of all expressions
- GradedModuleMap | GradedModuleMap -- a binary operator, often used for horizontal concatenation
- Iterator | Iterator (missing documentation)
- "Array | Array" -- see List | List -- join lists, sequences or arrays
- List | List -- join lists, sequences or arrays
- "Sequence | Sequence" -- see List | List -- join lists, sequences or arrays
- Matrix | Matrix -- join matrices horizontally
- "Matrix | Number" -- see Matrix | Matrix -- join matrices horizontally
- "Matrix | RingElement" -- see Matrix | Matrix -- join matrices horizontally
- "Number | Matrix" -- see Matrix | Matrix -- join matrices horizontally
- "RingElement | Matrix" -- see Matrix | Matrix -- join matrices horizontally
- "RingElement | RingElement" -- see Matrix | Matrix -- join matrices horizontally
- Net | Net -- join strings or nets
- "String | String" -- see Net | Net -- join strings or nets
- "String | ZZ" -- see Net | Net -- join strings or nets
- "ZZ | String" -- see Net | Net -- join strings or nets
- ZZ | ZZ -- logical or

This operator may be used as a binary operator in an expression like x|y. The user may install binary methods for handling such expressions with code such as

X | Y := (x,y) -> ...

where X is the class of x and Y is the class of y.