Definition
The portion of the wind blowing perpendicular (at 90 degrees) to the runway centerline or aircraft's intended track, expressed in knots. It is calculated from the total wind speed and the angle between the wind direction and the runway heading.
Plain English
The part of the wind that pushes you sideways across the runway, rather than straight down it. The bigger the angle between the wind and the runway, the more of the wind ends up shoving you sideways.
Context Anchor
Used when planning takeoffs and landings, especially when comparing the wind to what the airplane and pilot can safely handle.
Derivation
Crosswind comes from cross (across) plus wind. Component is from Latin componere, meaning 'to put together' -- here it means one piece of the total wind that has been split into two parts: the headwind/tailwind portion (along the runway) and the crosswind portion (across it).
Why Pilots Care
Exceeding the aircraft's maximum crosswind component can cause loss of directional control on takeoff or landing.
Grounding Statement
Picture the airplane rolling straight down the runway while part of the wind pushes across the runway from the left or right.
Intuition Check
Do not read crosswind component as the full wind speed. It is only the sideways part of the wind that affects the runway or aircraft direction.
Example Sentence 1
With the wind reported at 270 at 15 knots and runway 30 in use, the pilot calculated a crosswind component of about 8 knots -- well within the aircraft's limits.
Example Sentence 2
After recalculating with the updated wind, the pilot saw the crosswind component had risen above the demonstrated maximum.