What is the meaning of Theta?

The eighth letter of the Modern Greek alphabet, ninth in Old Greek: Θ, θ.

The measure of an angle.

Pitch angle; the angle between an aircraft's longitudinal axis and the horizontal plane.

The sensitivity of the value of a derivative with respect to time; the "time decay".

Designating a level of brain activity as measured by electroencephalography having a frequency of between four and seven cycles per second (associated with drowsiness in adults).

The voiceless dental fricative represented by θ.

theta; the Greek letter Θ (lowercase θ)

theta (Greek letter)

theta (Greek letter)

reliable

trustworthy

theta (Greek letter Θ, θ)

pre-reform spelling (used until 1943 in Brazil and 1911 in Portugal) of teta

theta; the Greek letter Θ, θ

Source: wiktionary.org