| Definition -
A way of categorizing verbs with respect to the semantic purpose of the sentence, e.g. whether the sentence is a command, a question, or a wish.
1. In contrast to aspect, which classifies verbs temporally, e.g. according to duration, repetition, and completion.
Some moods that exist or have existed in English are:
(1) optative mood: "Heaven forfend!" (used to expresses desire, archaic)
(2) indicative mood: "Bob is walking the dog." (used for factual statements)
(3) generic mood: "Turtles are slow." (used to make generalizations)
(4) imperative mood: "Let's go!" (expresses commands)
(5) subjunctive mood: "I suggested that David read some tea leaves." (used to discuss hypothetical events or to make polite requests, archaic)
(6) conditional mood: "If he leaves, I'll stay." (used to refer to events that will happen if something else it true)
(7) potential mood: "I may be seen" (indicates that something is possible, probable, or necessary)
Etymology - The term was coined by modifying the word mode (from the Latin modus, manner); thus, grammatical mood is unrelated to emotional mood.
Oxford English Dictionary - Its first citation in this sense is from 1573:
"How shall men directly fynde The Coniugation, Nomber, Person, Tence, And Moode of Verbes togither in their kynde?"
(Golding in Baret Alv. To Rdr. viii)