Literally meaning "looking at each other," an omiai (お見合い) is when two people are matched together by acquaintances. Traditionally, families will introduce their single son or daughter to their friend's offspring and go from there. Nowadays, however, a mutual friend called a sewanin (世話人, in this context meaning "mediator") will introduce a guy to a girl, both of whom are single and intent on finding a partner to settle down. Omiai has seen a dramatic decline in Japan as socialization between genders increases and online dating becomes more prevalent.
A mixture of nomikai (飲み会, drinking party) and omiai, gokon are similar to "Table of Six" meeting parties in some Western countries. Usually a guy and a girl plan a nomikai, each bringing an equal number of their friends of the same gender. It's a kind of group blind date where each person gets a chance to talk to everyone from the other side, asking questions and trying to find something in common. After the first event, there might be a second round, usually karaoke. Successful pairings will stay in touch and potentially develop into a relationship. Gokon are very common nowadays among the twenty-somethings and gay and lesbian gokon are growing in popularity as well.
Matchmaking agencies are still quite a big thing in Japan. Even though matchmaking as a profession still exists, more and more agencies now operate via the internet. Some of the bigger ones include Youbride and Match.com. Usually they charge a fee for membership.
We're going to assume you all know what these are and how they work. Many in their twenties and thirties nowadays are using dating apps and websites to find love, especially as they are generally free of charge. Tinder and OkCupid work fine in Japan, plus some local ones like Pairs and Matchbook. Thanks to your smartphone, love is now only a few feet away.