Terminals are used to connect electrical wiring to terminal strips, ground points, speaker lugs, circuit breakers etc etc etc.

There are many different types of terminals but because of the vibration in aviation we use mostly fully closed 'ring' type terminals rather than the 'forked' type terminals u see in many cars.

Then there are different types of terminals, the most commonly used terminals are the PIDG type terminals (pre-insulated diamond grip).
Insulated terminals are color coded for size. Wire conductor diameter can be measured in different ways but in aviation we use the american wire gauge standard (AWG). The higher the AWG number the smaller the conductor.

gauge 26-22: yellow
gauge 22-18: red
gauge 16-14: blue
gauge 12-10: yellow
gauge 8: red
gauge 6: blue
gauge 4: yellow
gauge 2: red
gauge 1/0: blue
gauge 2/0: yellow
gauge 4/0: blue

From left to right, the small yellow 26-22 gauge up to the large gauge 1 blue terminal.

The four on the left are PIDG type, the larger ones are TERMINYL type.
The PIDG type terminals are crimped with standard PIDG terminal crimptools.

Here's a close look of the PIDG (pre-insulated diamond grip) type terminal.
These terminals are designed to be reliable, easy to crimp and vibration resistant. These are pretty much the industry standard terminals and have a maximum temperature rating of 105C.

The PIDG terminals we use are for wires ranging from gauge 26 to gauge 10 and are by fare the most widely used terminal in aviation.

Here's a closer look at a AMPLI-BOND terminal.
This terminal is designed to be used in the 8 gauge to 4/0 gauge range, it is also vibration resistant and has a maximum temperature rating of 105C.

I haven't seen many of these ampli-bond type terminals around but there's no reason to assume that they are not up for the job.

A closer look at a TERMINYL type terminal.
Also a terminal designed for larger wires gauges in the same 8 gauge to 4/0 gauge range, high vibration resistant and high reliability and also has a maximum temperature rating of 105C.

Like the PIDG type terminals, the TERMINYL type terminals are also pretty widespread.

A solistrand uninsulated type terminal.
This terminal is designed to have a strong grip on variously shaped conductors, this terminal has a maximum temperature rating of 170C.

Here's a look at a couple of solistrand terminals.

A faston terminal.
Designed to be easily inserted onto a connection sleeve.

Faston terminals are easily removed and installed.

Copalum terminals and splices.
Copalum terminals and splices are designed especially for solving the inherent problems of terminating aluminum conductors. These connectors are terminated to stranded aluminum wire using a "dry crimp." This technique eliminates the need for an inhibitor agent to break down the highly tenacious and inert oxides that form on aluminum conductors.
See the copalum splice section for more information.

We use the copalum terminals and splices for generator wiring.

The Strato therm terminals.
These terminals are designed to withstand extreme heat, there are different types of these, the PIDG ones and the post insulated ones ranging around 288 degrees Celsius and the uninsulated ones should be able to withstand 649 degrees Celsius.

Having said that, u can imagine how hot these strato therm terminals must have gotten to get damaged like this.
These terminals were fitted to a logo light (a light that shines on the companies logo on the tail).