Ternary Form (ABA form) Theory Things   William Wieland
Sectional or Closed Ternary (A ends on tonic.)
Examples:
Twinkle, Twinkle Little Star 
Schumann "Humming Song" from Album for the Young op. 68 no. 3
Both A B A and A B A' are common. Da capo arias are in ternary form.

Sectional or closed ternary means that the A section begins and ends in tonic. In a continuous or open ternary form, the first A section would not end on tonic.

B often ends on V. B contrasts with A melodically, harmonically and/or texturally. B may develop motives or themes from A.

Repeat signs may occur, frequently   ||: A :||: B   A :||

Though A A' A'' and A B C each include three sections, A A' A'' features no contrasting middle section and A B C does not recapitulate the opening material.

Compound ternary is a three-part form in which each section is itself a binary or ternary form. Common examples include Minuet and Trio or Scherzo and Trio movements.