The distance between corresponding points on a wave separated by one period, e.g. the distance from peak to peak.

The number of waves passing a location per unit time.

The number of waves in a given unit of distance
OR
the number of waves in a distance 2π

The radiant energy transmitted in a radial direction per unit time.

The energy carried by electromagnetic radiation.

The radiant flux incident upon a surface per unit area.

The radiant energy radiated from a unit area per unit time.

The radiant flux radiated from a point source per unit solid angle in a radiant direction.

The radiant intensity per unit projected area in a radial direction.

The solid angle which, having its vertex at the centre of the sphere, cuts off an area equal to the square of the radius of the sphere.