What does it mean for a monitor to have a "DisplayPort out" connector?

I'm looking at this Dell monitor port layout:

Connectivity Options

Ports & Slots:
1. AC power connector | 2. HDMI connector | 3. DP connector (in) | 4. DP connector (out) | 5. Audio line-out port4 | 6. USB upstream port | 7. USB downstream ports (x1 with Power Charging) | 8. Stand lock | 9. USB downstream Ports (x1 with Power Charging)

So, I understand what USB upstream vs USB downstream means. But - what is "DisplayPort (out)" (as opposed to "DisplayPort (in)" which I'm used to)?

Solution 1:

This feature allows you to chain multiple Display Port Devices together. DisplayPort v1.2 allows daisy chainable displays to have both a DisplayPort input and a DisplayPort output. This includes multiple monitors, for example. Rather than having two cables coming from your PC, you can daisy chain two monitors and have less clutter and the use of shorter cables.

Solution 2:

DisplayPort allows displays to daisy-chained together in series rather than needing each display to be connected directly the computer itself.

In theory this can allow for simpler cabling in multi monitor situations where it might be difficult or messy to get multiple cables to the computer.

DisplayPort In will be the input from the computer, DisplayPort Out would be the output to other monitors.