The definition of "prayer" in the Oxford dictionary:
1 A solemn request for help or expression of thanks addressed to God
or another deity.
1.1 (prayers) A religious service, especially a regular one, at which people gather in order to pray together.
1.2 An earnest hope or wish.
A popular Buddhist prayer (based on the definition of "an earnest hope or wish") from the Karaniya Metta Sutta can be found below. The benefits of this prayer can be found in this answer.
Think: Happy, at rest,
may all beings be happy at heart.
Whatever beings there may be,
weak or strong, without exception,
long, large, middling, short,
subtle, blatant, seen & unseen,
near & far, born & seeking birth:
May all beings be happy at heart.
Let no one deceive another
or despise anyone anywhere,
or through anger or irritation
wish for another to suffer.
As a mother would risk her life
to protect her child, her only child,
even so should one cultivate a limitless heart
with regard to all beings.
With good will for the entire cosmos,
cultivate a limitless heart:
Above, below, & all around, unobstructed,
without enmity or hate.
Whether standing, walking,
sitting, or lying down,
as long as one is alert,
one should be resolved on this mindfulness.
This is called a sublime abiding
here & now.