An area attack is an attack that targets an area, rather than a specific creature or group of creatures. There are four kinds of area attacks: Arcs, Lines, Cones, and Bursts.
An Arc is an area attack that contains a number of spaces, each of which (except for the two endpoints) must be non-diagonally adjacent to exactly two other spaces in the arc, and each of which must be adjacent to the origin space.
A Line is an area attack that contains a number of spaces, each of which (except for the two endpoints) must be adjacent to exactly two other spaces in the line. A 'close line 5' is a 5-space line where one of the endpoints must be adjacent to the creature or object causing the line effect, while a 'line 7 within 4 paces' is a 7-space line where each of the line's spaces must be within 4 paces of the creature or object causing the line effect. A close line resolves forced movement and line-of-effect from the originator's square, while a line that is detached from its originator resolves forced movement and line-of-effect from the closest space within the line.
A Cone is an area attack that spreads out from a point in a roughly 90-degree arc. For the sake of simplicity, a 'cone' is a square area, one corner or side of which touches the corner or side of the origin space. An 'adjacent cone 2' attack uses the effect creator's space as the cone's origin space, while a 'cone 2 within 5 paces' uses a space within 5 paces as the cone's origin space.
The cone's number determines the length and width of the area, so a 'cone 4' is a 4x4 space area touching the origin space on one corner or side. A cone reaches a maximum height equal to its length and width.
Unlike spherical bursts, cone attacks use the 'square area' abstraction regardless of whether the true distance optional rules are in effect - the difference is rarely more than a single space at the corner of the blast.
Each target within the cone's area checks line of effect from the creature or effect that is casting the cone, not the origin point of the cone itself. For adjacent cone attacks, this will be the same space, but for ranged cone attacks this difference may become important.
A burst is an area attack that spreads out spherically from a point in space. A burst will always specify an origin space; all line-of-effect and forced movement effects are resolved from that origin space. The number determines the radius of the burst area, not including the center space itself, so a 'burst 1' includes the origin space and each adjacent space, while a 'burst 5' includes the origin space and each space within 5 paces of it.
For burst attacks, it is important to note whether the true distance optional rule is being used - this will determine whether bursts are resolved as simple squares, or actual circular areas.