Katakana are a set of phonetic Japanese characters, sometimes referred to as a syllabary. This is one of the two sets of kana; Hiragana being the other.
Katakana can typically be differentiated from Kanji and Hiragana by their simplicity and angular lines. Hiragana being more curvy and Kanji usually having more strokes.
Katakana has multiple uses:
- Spelling out foreign words loan words. (i.e., Ramen: Chinese, Table: English, Chou Creme: French, Albeit: German, …)
- Providing readings for names. Japanese names are particularly difficult to read and hence most forms require one to write the reading of their name in small Katakana characters. I don't know why Katakana was chosen over Hiragana, but it seems to be the standard. These small guidance-giving characters are usually called Furigana.
- Spelling out scientific words. Often names of plants and animals are written in Katakana, even if the name is Japanese and has a Kanji writing.
- Grabbing attention in advertising. Since the usage of Katakana was limited, it stood out in print. In the 80's and 90's this practice grew to the point that it lost effectiveness. Roman characters are now also being used for attention getting.
All of the Katakana characters are simplified versions of Kanji written in cursive.