There is some confusion about the spelling of oolong tea. Some prefer oolong tea while others prefer wulong tea. Other common spellings include wu long tea and wu lung tea.
Both "oolong tea" and "wulong tea" refer to the same type of tea. Even if it is spelt "wu long tea" or broken into "wu long", it is still the same type of tea.
Why so many spellings?
The simple reason is that "wulong" is a Chinese word, and the Chinese language does not use an alphabet. Unlike English or most other Western languages, written Chinese uses characters which represent entire syllables (more accurately each character is morphemo-syllabic).
The spelling "wulong" (or "oolong" or "wulung") is a phonetic transcription of the Chinese characters that approximates the sound of spoken Chinese - more specifically spoken Mandarin.
The Chinese characters for oolong tea (or wulong tea or wu long tea) are these:
The first character is pronounced "oo" or "wu". The second character is pronounced "long" and the third character (tea) is pronounced "cha".
There are several different systems for Romanizing the Mandarin language. Romanization is the process of transcribing the sounds of spoken Chinese with letters from the Roman alphabet. Western students of Mandarin Chinese can use Romanization to help them learn to speak the language without first having to learn thousands of different Chinese characters.
Most of the world (including China and the UN) has adopted Pinyin as the Romanization system for Mandarin Chinese. Chinese children learn pinyin before learning to write Chinese characters. If you look at a Chinese children's book, it will have pinyin written above each character.
Taiwan still doesn't have any one Romanization standard and Romanization is not used to teach Taiwanese children. Children's books in Taiwan use a system called Zhuyin (or Bopomofo), which is an phonetic alphabet made out of components of Chinese characters.
The correct pinyin transcription of 烏龍茶 is "wulong cha". Since Mandarin is a tonal language, pinyin written in books for children or foreign students usually has tone marks written above it. With tone marks, it is wū lóng chá. The way to write 烏龍茶 in zhuyin is ㄨ ㄌㄨㄥˊ ㄔㄚˊ.
If you see Chinese words that are spelled differently from the pinyin standard, they were probably imported into the English speaking world via Taiwan, or else they have been in use since before Pinyin was common. It is also possible that they came from another another language, such as Cantonese or Japanese.