Fill-Flash: When photographing in strong sunlight or backlighting, deep shadows can be cast across the subject. Fill-Flash (or Forced Flash) works with the ambient light to ‘fill-in’ the shadows without overexposing the image.
FP/High Speed: Some cameras, or flashguns, offer high-speed sync, which lets you exceed your flash sync speed. It’s a huge advantage if you need to shoot using flash in bright daylight at wide aperture settings.
Flash Exposure Compensation: You can use this setting, located either in the camera’s menu system or flashgun depending on your model, to override the flash output by increasing (+EV) or decreasing (-EV) the flash exposure when its set to Auto or TTL mode.
Red-eye reduction: Some cameras offer red-eye reduction mode, which helps reduce red eye caused by the light from the flash hitting the subject’s retina. It’s most prevalent in subjects with blue eyes but can be fixed with editing.
Slow-sync: Normally when you fire the flash the subject is well lit but the background is rendered black, Slow-Sync mode keeps the shutter open for longer to allow ambient light to be recorded. It's often best to use Second-Curtain Sync with Slow-Sync mode.
Second-curtain sync: Also known as Rear-Curtain Sync, this mode sets when the flash fires during a slow exposure. Normally flash will fire at the beginning of an exposure to freeze the subject but this creates motion blur in front of the subject, which can look odd. Second-Curtain Sync fires a burst of flash at the end of the exposure so any motion blur travels behind the subject rather than in front.
Manual flash: Instead of letting the camera determine the flash power output, manual mode allows you to control the power of the flash in fractions: 1/128, 1/64, 1/32, 1/16, 1/4, 1/2 and 1/1 (full power). You set the flash sync speed then work the flash power for the perfect exposure.
Wireless (Slave/master): When using multiple off-camera flashguns, your master flash triggers the slave flashes to fire. You can also group flashguns for the ultimate control.
Stroboscopic flash/ Repeating flash: In this mode the flash fires continuously to record the subject multiple times during an exposure to reveal movement in one frame.