Pocket dialing occurs when a person accidentally dials or calls a number while the phone is in his or her pocket or bag.The receiver then answers the call and hears noises in the background, but there is no one on the line. Pocket dialing has become an inconvenience and may cause humiliation because the recipient of the call could overhear private conversations or anything occurring in the caller's vicinity.
This is also known as butt dialing or pocket calling.
Techopedia explains Pocket Dialing
A pocket dial is often activated when objects in the caller's bag or pocket make contact with the phone’s buttons. This usually results in a call to someone on the caller's contact list, because they can be dialed at the touch of a button.
Although pocket dialing is mostly annoying or embarrassing, some instances are more serious, such as when emergency numbers like 911 are dialed. Because the caller is not aware of the call and can't provide information to the 911 operator, emergency services are often dispatched to ensure the caller is not in real trouble. Since touch interface phones have made pocket dialing more of a problem, applications for smartphones have been developed to prevent this. Newer smartphones with capacitive touchscreens are less susceptible to this because the screen does not react to most non-conductive materials. These phones also have smart software, which detects activity and locks the phone after a set amount of time if the screen is not used.