Leave it to our sport to really complicate matters related to love.
In tennis, “love” means zero. Scoring in tennis isn’t like most other sports that follow a linear one, two, three type of progression.
When starting a game or a set, a rational person would think “it’s zero-zero”. That would be true. But in tennis, we say “love-love”. And when you win a point, it’s not 1-0 or one-zero…it’s 15-love.
It begs the question of why the word was introduced into the sport of tennis at all. Where did it come from and why?
The answer is that there really isn’t a well-defined, universally-accepted reason or rationale behind it. It’s not perfectly clear how this usage of love came to be. The three most popular commonly-held beliefs are:
1) Tennis players are overly passionate! One of the most accepted theories is that those with zero points were still playing for the "love of the game" despite their losing score.
2) Somewhat related, the Oxford English Dictionary suggests that the term might be rooted in the colloquial phrase “for love,” meaning “without stakes being wagered.” This theory reflects the sport’s long history of etiquette and sportsmanship.
3) Others theorize that love arose from the French word for “egg,” l’oeuf, because a zero on a scoreboard resembles an egg. This claim remains unsubstantiated but given the sport’s roots in France about 900 years ago, it seems entirely plausible.
The idea is that a person who fails to make any points doesn't care because they are playing for love of the game, rather than playing to win (which, really, every player is trying to do but when you can't get it together at least show good sportsmanship and play for love) or playing for monetary stakes. In other words, playing on the court, challenging yourself, is the reason for still playing despite having the score of love. And to players of tennis, the sport can be truly a "labor of love," an expression which implies an undertaking performed out of love for the work itself without consideration of benefit or reward. A similar idea is found in the origin of the word amateur, which can refer to a person who does something strictly for love; the word comes from the Latin word amare, meaning "to love."
This last point is the one we think is most probable.
