Every new market mania needs new metrics to attract investors and explain the reason for its existence. Here’s one for the bitcoin boom: “BTC yield.”

MicroStrategy, which once was a humdrum software firm, introduced this unusual term to its investors in August. BTC, for the uninitiated, means bitcoin. Yield typically refers to the dividend a company pays as a percentage of its stock price, or to the interest rate a lender expects to earn on a loan or bond. This isn’t either of those.