What is pitch?
Pitch may refer to several things, the first of which is a quality of sound. The pitch of sound refers to how high or low we perceive a sound to be based on the frequency of the sound waves. Pitch is also the term used to describe a kind of resin derived from burning plants or which results from decayed organic matter. We also call this viscous substance tar, asphalt, or bitumen, and it may be used to seal roads or structures. As a verb, pitch can refer to throwing, as in baseball. Finally, the term "pitch" may also be used to describe an incline or slope of some kind. In flight, rotation around the side-to-side axis, which creates a slope, is called pitch.
In addition to what was noted in the answer above, pitch may also refer to a sales pitch, which is a persuasive talk or presentation that aims to motivate a person or company to purchase a product or service. This can be an elevator pitch, a short, pithy persuasive talk that sums up the importance of a product or service in however much time (usually less than a minute) that it takes a person to ride an elevator to his destination. This version of pitch dates to 1943 and may derive from the idea of pitching or throwing a baseball. This could also refer back to pitch's 1847 definition of "to work vigorously."
The word, going back to the 1200s, can also mean to set something up or fasten it in place, hence the origin of the term we still use, pitch a tent.