Whats the meaning of "gt" and "lte" in the field called "monitor.timespan"?

Elastic Stack Beats
1

Hello!
I just see in "heartbeat" index a field called "monitor.timespan" which contains the following:

{
  "lt": "2021-06-11T09:58:59.034Z",
  "gte": "2021-06-11T09:58:54.034Z"
}

What's the meaning of "lt" and "gte"? I would like to know if some of this dates simbolize the exactly moment when heartbeat checks the status of the monitor.
Thanks in advance

2

"Less than" and "greater than or equal", so the timespan represents time between 2021-06-11 09:58:54.034 and 2021-06-11 09:59:59.034 (though not including the exact millisecond of the latter.)