katakana カタカナ

The katakana 片仮名 is one of the three Japanese "alphabets". It's counterpart of the hiragana ひらがな. Both katakana and hiragana are sometimes referred to as kana かな.

Unlike the kanji 漢字, whose readings may vary depending on the word, the way a kana such as katakana is read always stay the same.

The katakana is normally used to write loan-words, foreign (non-Japanese) names, onomatopoeic and mimetic words, the readings of kanji and words in online dictionaries, and to indicate speech sounds off (e.g. mispronounced, or badly pronounced, like a robot talking) in manga. Aesthetically, it looks cooler than the other "alphabets."

• Chart

Chart

For reference, the romaji chart including only the katakana:

a ア	i イ	u ウ	e エ	o オ
ka カ	ki キ	ku ク	ke ケ	ko コ
ga ガ	gi ギ	gu グ	ge ゲ	go ゴ
sa サ	shi シ	su ス	se セ	so ソ
za ザ	ji ジ	zu ズ	ze ゼ	zo ゾ
ta タ	chi チ	tsu ツ	te テ	to ト
da ダ	di ヂ	dzu ヅ	de デ	do ド
na ナ	ni ニ	nu ヌ	ne ネ	no ノ
ha ハ	hi ヒ	fu フ	he ヘ	ho ホ
ba バ	bi ビ	bu ブ	be ベ	bo ボ
pa パ	pi ピ	pu プ	pe ペ	po ポ
ma マ	mi ミ	mu ム	me メ	mo モ
ya ヤ		yu ユ		yo ヨ
ra ラ	ri リ	ru ル	re レ	ro ロ
wa ワ		n ン		wo ヲ

Some notes:

• The layout above is called gojūon 五十音, "fifty sounds," although it's only really fifty without diacritics.
• Different romaji systems have different romaji for the same kana, e.g. フ is fu in some systems, hu in others.
• zi-di-zu-dzu シヂズヅ, known as yotsugana 四つ仮名, are pronounced identically in some regions of Japan.
• The small a-i-u-e-o ァィゥェォ may be used to mark long vowels.
• The small tsu ッ may be used to mark geminate consonants.
• The small ke ヶ isn't a katakana but a symbol instead.
• vu ヴ, u ウ with dakuten 濁点, is a syllable found only in foreign words, meaning that, in practice, it's as if it had no hiragana counterpart, as hiragana isn't normally used to write foreign words.

Next you have the diphthongs (compound kana) spelled using the small kana ゃゅょ.

kya キャ	kyu キュ	kyo キョ
gya ギャ	gyu ギュ	gyo ギョ
sha シャ	shu シュ	sho ショ
ja ジャ	ju ジュ	jo ジョ
cha チャ	chu チュ	cho チョ
dya ヂャ	dyu ヂュ	dyo ヂョ
nya ニャ	nyu ニュ	nyo ニョ
hya ヒャ	hyu ヒュ	hyo ヒョ
bya ビャ	byu ビュ	byo ビョ
pya ピャ	pyu ピュ	pyo ピョ
mya ミャ	myu ミュ	myo ミョ
rya リャ	ryu リュ	ryo リョ

For reference, as an image:

Source: japanesewithanime.com (CC BY-SA 4.0)