An airfield traffic pattern is a standard path followed by aircraft when taking off or landing while maintaining visual contact with the airfield.

At an airport, the pattern (or circuit) is a standard path for coordinating air traffic. It differs from "straight-in approaches" and "direct climb-outs" in that aircraft using a traffic pattern remain close to the airport. Patterns are usually employed at small general aviation (GA) airfields and military airbases. Many large controlled airports avoid the system unless there is GA activity as well as commercial flights. However, some kind of a pattern may be used at airports in some cases such as when an aircraft is required to go around, but this kind of pattern at controlled airports may be very different in form, shape, and purpose to the standard traffic pattern as used at GA airports.

The use of a pattern at airfields is for aviation safety. By using a consistent flight pattern, pilots will know from where to expect other air traffic and be able to see and avoid it. Pilots flying under visual flight rules (VFR) may not be separated by air traffic control, so this consistent predictable pattern is a vital way to keep things orderly. At tower-controlled airports, air traffic control (ATC) may provide traffic advisories for VFR flights on a work-load permitting basis.
How important is pilot communication with a non-towered controlled airport?
Piloting into a non-towered airport in my experience can be more challenging than towered airports.  What makes it challenging is that you are not speaking to anyone in charge of the airspace.  You are broadcasting to an open communications channel and hope all the other pilots “play” by the rules.  The first best practice is to have a basic understanding of the airport, how many runways, what direction do they run, direction of the traffic pattern and traffic pattern altitude etc.?   Practice consistency as this will aid in your decision making process.  As you approach the airport you must also check the weather via AWOS or ASOS to determine the wind direction, speed and altimeter setting.  The next step is to tune into airport UNICOM to listen to other traffic in the area, note the departures and arrivals and also note other planes in the traffic pattern.  The next step is to identify yourself via the airport UNICOM channel, provide your distance to the airport and your direction from the airport.   Your approach direction will most likely determine how and where you will join the traffic pattern.  Most importantly, keep listening to the airport UNICOM and actively look for any other planes either in the traffic pattern or in the vicinity.  There are a minimum of 4 traffic pattern legs - crosswind, downwind, base and final.  Your job as a pilot is to communicate as you enter each pattern leg. It is also beneficial to communicate your intentions whether you are executing a full stop landing or a touch-n-go.  If you are doing a full-stop landing be sure to communicate when you are clear of the given runway.