Invitations to the theatre, concert, and garden party, are mostly informal affairs and are sent as brief letters.
A garden party is a sort of out-of-doors at home.
To a garden party which is not formal or elaborate
Locust Lawn,
June 29, 1922.
My dear Miss Burton,
Will you come to tea with me informally on the lawn on Thursday afternoon, July the fourth, at four o'clock? I know you always enjoy tennis and I have asked a few enthusiasts. Do try to come.
Cordially yours,
Ruth L. Anson.
Such an invitation is acknowledged in kind—by an informal note.