Mnemonics

"include", "or", "interpolate"

• Captures
• any junctions
• inclusive or

Used alone

| as a prefix coerces to a Capture which is useful for argument list interpolation (also see here)
| between items creates an any junction

Operators containing this character

~| and +| and ?| A bitwise inclusive or
|| A tight short circuit inclusive or

When used inside regexes

| splits lists of Alternatives
|| does the same but behaves closer to what | did in perl5

Other Uses

| in a Signature can grab arguments in their raw Capture form
| is a vertical line in POD tables

Old, deprecated, or other language uses

$| is the autoflush default in perl5