Answer:

Definition: Given two points on a circle, the minor ARC is the shortest arc linking them. The major arc is the longest.

Try this Drag one of the orange dots. Note how the points define both a major and minor arc.

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Two points LYING on a circle actually define two arcs. The shortest is called the 'minor arc' the longer one is called the 'major arc'. In the figure above, if you were to refer to the 'arc AB' you could mean either one. Typically, if you don't specify which, readers will assume you mean the minor (shortest) arc. If there is a POSSIBILITY of confusion, you should state which one you mean.

Another way to avoid confusion is to have another point on the arc and use all three to define it. For example 'arc AQB', would not be in doubt SINCE the point Q would lie on only on one of the two possible arcs.

When the major and minor arcs are the same length, they divide the circle into two semicircular arcs. 

See Semicircle definition. Under these circumstances neither arc is considered to be the major or minor arc.

Other circle topics

General

Circle definition

Radius of a circle

Diameter of a circle

Circumference of a circle

Parts of a circle (diagram)

Semicircle definition

Tangent

Secant

Chord

Intersecting chords theorem

Intersecting secant lengths theorem

Intersecting secant angles theorem

Area of a circle

Concentric circles

Annulus

Area of an annulus

Sector of a circle

Area of a circle sector

Segment of a circle

Area of a circle segment (given central angle)

Area of a circle segment (given segment height)

Equations of a circle

Basic Equation of a Circle (Center at origin)

General Equation of a Circle (Center anywhere)

Parametric Equation of a Circle

Angles in a circle

Inscribed angle

Central angle

Central angle theorem

Arcs

Arc

Arc length

Arc angle measure

Adjacent arcs

Major/minor arcs

Intercepted Arc

Sector of a circle

Radius of an arc or segment, given height/width

Sagitta - height of an arc or segment