also: よう · よお
Casual, friendly call to get someone's attention or greet them. Often used among friends or in informal situations.
よー、元気か？
Hey, how are you?
よー、久しぶりだな！
Yo, long time no see!
Come on, hurry up and come!
大丈夫だよー、心配するな。
It's okay, hey, don't worry.
おい is a blunter, often male-associated call for attention, whereas よー sounds friendlier and is used more casually among peers of any gender.
Variant spelling with お; also represents the lengthened sound.
Standard hiragana spelling; less emphatic than よー.
Lengthened form of the interjection/particle よ, used for added emphasis or friendliness. The exact origin of よ itself is uncertain, but it has been used as a sentence-final particle since at least the Edo period.