What does "lap" mean in swimming?

About a year ago, I didn't know how to swim. Any pool that's deeper than 5 ft. scares me. Haha...  Then I mustered the courage to take up swimming lessons and learned.   I continued to practice and watched video tutorials until I could comfortably swim across 25 meters.

Recently, I made my first attempt to swim in an Olympic-size pool.   Could I swim across 50 meters? Guess what? I successfully did!  12 laps in total.  Yay!

50m Pool at the Makati Aqua Sports Arena (MASA)

Then as I was writing this, I thought of googling what does a "lap" mean in swimming coz I'm a newbie and I might be misusing the term.  I ended up reading several discussions among professional swimmers and long-time swimmers across the globe.  Ironically, the definition of lap is an open debate.

Here are the various definitions of lap being debated in forums:

• A lap is 1-way - getting across the pool.  (This is also how one Olympic swimmer defined it in an interview.) 
• A lap is 2-way - up and back.  If you swim 1-way only, it's called a length. Thus, 2 lengths is equal to 1 lap.
• A lap is swimming around the perimeter of the pool. 
• A lap is 50 yards.
• A lap is 50 meters.
• Lap and length can be used interchangeably to mean swimming across the pool 1-way.
• Never use lap for swimming, only use length. 

Crazy, right?!  Sadly, I couldn't find a source where the definition of lap in swimming was made official.  :(

But wait, before you conclude I swam 1.2 kilometers (if your definition of a lap is 2-way), that's not what I meant!  Wahaha....   When I wrote it, my definition of a lap was 1-way.   Haha....  And I wasn't really tired yet but my friend and I were starving already so we decided to have all-you-can-eat shabu-shabu right after.   Haha....

I guess when you're using the word lap in swimming, it's better to qualify it by declaring the length of the pool coz the difference in the conflicting definitions is big -  one person could easily interpret it as half or twice the actual distance swam.  :)