What is meant by inclination of the earth?

The Earth rotates round the Sun in a orbit that defines the 'Plane of the Ecliptic'. The spin axis of the Earth is inclined approx 67.5 degrees from the Plane of the Ecliptic. This inclination determines how far North and South of the Equator the Sun will be vertically overhead at least one day of the year. So the Tropics of Cancer and of Capricorn; those places; are 22.5 deg distant from the Equator. [90 - 22.5].