According to Wikipedia:

Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an endoscope, an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ. Endoscopy can also refer to using a borescope in technical situations where direct line of-sight observation is not feasible.

Endoscopy has different uses. In can be done in gastrointestinal tract (GI tract) examination. This nonsurgical method is being used to check a person’s digestive tract with the use of an endoscope – a flexible pipe with a light and camera attached. The images captured by the camera of your digestive tract is being transmitted and viewed on a monitor. But once the procedure is set to the small intestine, it is then called enteroscopy.

In an esophagogastroduodenoscopy procedure, the endoscope is inserted to the mouth and throat and into the esophagus. This set the doctor to see the esophagus, stomach, and upper area of the small intestine.

In a similar matter, during a sigmoidoscopy or colonoscopy procedure, the endoscope can be inserted into the large intestine/colon and examine it passing through the the rectum.

ERCP (Endoscopic Retrograde CholangioPancreaticography) is another form of endoscopy that examines the bile duct and its neighboring organs.

Rectoscopy and Anoscopy examines the rectum and anus respectively. Both are also referred to as Proctoscopy.

Endoscopic ultrasound or EUS combines upper endoscopy further ultrasound examination to obtain images and information about various parts of the digestive tract.

An endoscope can consist of:

• a rigid or flexible tube
• a light delivery system to illuminate the organ or object under inspection. The light source is normally outside the body and the light is typically directed via an optical fiber system
• a lens system transmitting the image to the viewer from the objective lens to the viewer, typically a relay lens system in the case of rigid endoscopes or a bundle of fiberoptics in the case of a fiberscope
• an eyepiece
• an additional channel to allow entry of medical instruments or manipulators