In the prelude to the questions, we gave away the fact this is a type of
tubing. But of course the name gives that away also. We also gave away that it's flexible and liquidtight. What we didn't give away is its defining characteristics (though we did mention some of them). As the name tells us, it's also metallic.
Flexible Metallic Tubing (FMT) [360.1, 360.2] is an unthreaded, metallic, liquidtight raceway of circular cross section. It may be ferrous (made of steel) or nonferrous (made of aluminum). Many people mistakenly think that because it's metallic, it can be used as a "grounding" (bonding) path. But because there's so little electrical contact at the connectors and because those connectors can work loose, that is not the case. Run your bonding jumper inside your FMT (and, of course, in the EMT you are connecting it to).
360 lists four permitted uses [360.10]. That would seem rather limiting, but the number of installations that qualify is significant. Partly, that's because 360.10 is quite vague. For example, you can use it in concealed spaces. This makes it ideal for (as an example) connecting raceway to overhead lights. You cannot use flexible cord in the spaces above ceilings, because rats, mice, members of Congress, and other rodents can chew through the insulation (as can raccoons, cockroaches, ants, etc.) and set things up for a lovely arc flash that causes the whole building to burn up. Generally speaking, building owners prefer their buildings not to be burned down. To understand the many applications where you can use FMT, it helps to look at the six prohibited uses. Looking at where it can be used can also help you understand where it cannot be used (for example, you can use it for system voltages of 1000V maximum, which means you can't use it at higher system voltages).
360 lists six prohibited uses [360.12]. If you look at that list, it totally makes sense because of the nature of this tubing. For example, it doesn't seal so you can't use it in a battery room where gases could enter the tubing if you did install it there.
install FMT using approved methods. Article 360 gives explicit commentary regarding
bending, bend radii, number of
bends, trimming, supporting, securing, and other facets of installation [360.24 - 360.42]. Make sure you adhere strictly to the minimum radii specified in Table 360.24(A) and Table 360.24(B). Note that these are absolute minimums, to be followed at all times not just after you get the FMT in place. If someone kinks the FMT or steps on it, toss out the damaged FMT and use a new length of it.
You can use
only fittings that are listed for use with FMT [360.42].