Mnemonics

"arrow", "less", sideways "V" for "values"

• has multiple uses
• for << see « instead

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Used alone

• < as an infix operator performs a comparison

Used as a brace pair or quote pair

• <> is shorthand for the qw quoted array constructor, providing string context
• <> can "treat things as a hash", providing an uninterpolated string context as was the default in perl5. (e.g. %hash<value>)
• <> can be used in adverbial pair constructors in place of {}, providing uninterpolated string context (e.g. :key<value>)

Operators containing this character

• <= is a comparison. Note this means there is no assignment mutation.
• ~< +< and ?< left bitwise shifts
• <== or <<== a feed operator («== is not)
• $< a twigil, shorthand for using named matches.

When used in a regular expression

• < Introduces a subrule
• <( The start of a result
• <> Introduces extensible metasyntax

Other uses

• << can be used as a "Texas Quote", a substitute for « (left french quote) in environments where unicode source code is undesireable. See that character's page.
• "prefix:<>" "postfix:<>" "infix:<>" The extended identifier of an operator.

Old, deprecated, or other language uses

• << is bitwise shift in many languages including perl5. That is now +<, ~<, or ?<
• (?< in perl5 introduced some regular expression extension syntax. Those have all changed drastically.