More rigorous definitions can be found in almost any book on the subject. A set of orbital elements is a snapshot, at a particular time, of the orbit of a satellite. Epoch is simply a number which specifies the time at which the snapshot was taken. The orbit ellipse lies in a plane known as the orbital plane. The orbital plane always goes through the center of the earth, but may be tilted any angle relative to the equator.
Inclination is the angle between the orbital plane and the equatorial plane.
By convention, inclination is a number between 0 and 180 degrees. The intersection of the equatorial plane and the orbital plane is a line which is called the line of nodes. More about that later. Two numbers orient the orbital plane in space. The first number was Inclination.