At 11:59pm tonight an extra second will be added to the passage of time.
Why? Who better to give you a TL;DR explanation than Sean Shannon, the Guinness World Record holder for fast talking with a rate of 655 words per minute (about 10 or 11 words a second), who we asked to sum it up in under one second.
That's right: "Earth's weird spin adds extra second."
For more than one second’s worth of detail, we'll let the Independent's technology reporter Andrew Griffin explain:
On June 30, clocks will count all the way up to 11.59.60, giving the day an extra second. That’ll help the Earth’s irregular rotation catch up with atomic clocks’ highly precise one, stopping them from getting out of sync.
The extra second might seem unimportant, but can cause huge problems for computers. Some have proposed getting rid of the idea entirely — but the UK has argued that we should hold on to it.