"Our" compatibility means that there is at least one directional passive (not powered) interface between two active (powered) devices.
Example 1. A camcorder with a Firewire output is compatible with a recorder with a Firewire input.
If one device is passive it can be directly connected to the other device.
Example 2. A camcorder with a Firewire 4 pin female connector is compatible with a 4 pin Firewire male plug.
We think that "absolute" compatibility is unreachable. We think that any two compatible devices will always have an imaginable interface which works with one and does not work with the other.
Example 3. A camcorder has both Firewire and SDI outputs and a recorder has Firewire input but no SDI input. So they are compatible through Firewire but not compatible through SDI. We will still list them as "compatible".
Please note we do not consider all possible interfaces for each device, but only those we consider important.
The above means that if you need a specific compatibility between two devices you should not rely on our "common sense" compatibility.
Example 4. Dangerous Compatibility. If your camera is equipped with Firewire please do not be in a hurry to connect it to your computer's Firewire. Hot-plugging (when both devices are switched on) the camera to the computer using Firewire may burn the camera's Firewire output together with its main board. Our website does not show such compatibility. We do not recommend using Firewire to connect video equipment with computers at all.
Example 5. Cross Brand Compatibility. Third party accessories may have high quality and an attractive price. For example, Globalmediapro batteries will perfectly work with compatible camcorders but Globalmediapro batteries will live much longer if charged with Globalmediapro chargers. In the case of Globalmediapro batteries, our website shows when cross brand compatibility works and when it does not work. At the same time, we may omit some useful cross brand compatibility for other products. (See also: How to choose batteries and chargers?)
Example 6. Formally Compatible. Consider a very small camera and a very large carrying case. Are they compatible? Formally they are compatible. We try to show compatibility only when the camera tightly fits into the case. This is a difficult call for an online shop.
Example 7. Incompatible But Useful. We cannot declare a studio light compatible with a video camera. They have no common interfaces. Though the studio light is useful.
Example 8. Formally Compatible. Consider a camera light equipped with a battery mount. The light may be compatible with your camera but incompatible with your battery fleet. If you purchase such a light you will have to purchase an extra battery and charger to power it. Since we cannot know what batteries you have, we show cameras compatible with camera lights regardless their battery mounts. (See also: How to choose a camcorder light?)