What is NTSC / PAL / SECAM?

NTSC / PAL / SECAM 

Due to the frequency difference of the AC currents of different regions we end up with these two different video recording formats.

NTSC

North America, parts of South America, Japan, Taiwan, the Philippines, and South Korea have AC current at 60Hz, this is the same vertical frequency which is in the NTSC format (NTSC being an abbreviation of National Television System Committee) The frame rates for these are usually half the frequency so you will often see NTSC recorded at 29.97/30FPS

PAL / SECAM

Australia, most of Western Europe, China, some parts of Africa, India, and elsewhere have AC current at 50Hz which is the same vertical frequency as PAL (Standing for Phase Alternation by Line) or SECAM (Sequential Color with Memory) which is in France, Russia, and parts of Africa. Just like NTSC, the relationship between Hz and frame rate is often half, The TV broadcast standards for PAL and SECAM are shot at 25FPS.

Both NTSC, PAL and SECAM are television standards and are different to 23.976/23.98/24FPS which is what film stock was projected at. 

PAL/SECAM Relationship

You will often see PAL/SECAM because though they are different formats they both have frame rates at 25FPS because the AC currents of all the countries that use both PAL and SECAM are at 50Hz. This means they can often be written together.