Reflexive property

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A relation R on set A is reflexive if for every x in A, x R x.

This can be written in mathematical form as follows.

$Reflexive property$
This is read as "for all x in (set) A, (condition) x R x (is true)"

Universal quantification involves "for all" within a certain domain set.

The symbol "∀" is read as "for all".
An example is as follows.

∀ x ∈ { 1 , 3 , 5 } : x is an odd number

This is read as "for all x in the set 1, 3, 5, x is an odd number"

The symbol "∈" is read as "in" which is short for "is an element of" (the domain set that follows).
The symbol ":" (colon) can be thought of as saying "such that" or "it is true that" (what follows).

More: Peano: symbols

More: Everything and all things: But wait, there's more

An example of a reflexive rule is the following.

It is good to be able to laugh at oneself.

Have you heard that being able to laugh at yourself may help lengthen your life?

Here, the "laugh at" relation is applied reflexively to itself. That is, relating "laugh at" from "you" to "you".

Have you heard that laughing at your spouse may help shorten your life?

Here, the "laugh at" relation is not applied reflexively.