What is a Power Ranger?
A Power Ranger is a person who morphs from an unpowered form into a powerful superhero wearing a brightly colored battle suit featuring a helmet with an opaque visor; in many cases, the helmet serves to protect his or her secret identity. A morphed Ranger generally possesses superhuman strength, durability, and hand-to-hand combat ability; unmorphed Rangers may possess other innate abilities (such as telepathy, super speed, invisibility, great hand-to-hand combat ability, etc.) that are usually not directly related to his or her Ranger powers.
Rangers appear to retain their original physiology beneath their suits when in morphed form, as Rangers' helmets have been seen removed or broken on numerous occasions, revealing his or her natural form underneath (there are exceptions to this rule: Justin, the Blue Turbo Ranger, was in his early teens and was much shorter than his Ranger form when unmorphed; Anubis "Doggie" Cruger, the S.P.D. Shadow Ranger, has a muzzle [he is a humanoid dog-like alien] that seems to disappear beneath the helmet; and Daggeron, the Solaris Knight, transforms into his Ancient Mystic Mode while in the process of morphing). Helmets aside, the suits are donned and removed nearly instantaneously with a glow of light or some other effect. Sometimes, Rangers "de-morph" involuntarily due to powerful physical attacks.
Rangers regularly operate in teams of five, with a special sixth Ranger frequently joining the team part way into the series; sometimes a core team of three will later be joined by additional Rangers. Each Ranger's suit and energy spectrum will match a specific color, with red, yellow, and blue being joined by some combination of pink, green, black, or white. Rangers may be named after their respective colors, such as Red Ranger, Blue Ranger, etc., but numbers or other names may also be used. There is usually no more than one Ranger of a given color on a team, but exceptions of this rule are generally given alternate names (in Time Force, there were two Rangers with red-colored costumes; the first was the Red Time Force Ranger, the second was the Quantum Ranger). The team's costumes are nearly identical aside from color, helmet design (most notably the shape of the opaque visor) and perhaps a numerical designation; any additional Rangers will regularly have additional costume modifications, usually some form of additional armor.
The Rangers' color designation also influences their wardrobe throughout the series, as their civilian clothing is often the same color as their Ranger color. This correlation was joked about in Dino Thunder when Tommy Oliver (a former Green Ranger, White Ranger, and twice a Red Ranger) became the new Black Dino Ranger; he said that he had to go shopping because he did not own enough black-colored clothing.