As Rick pointed out, it's the Diamond Model of Intrusion.
Look at the image as if it is telling a story.
Solid lines are referring to actual events. Dotted lines are hypotheses.
Let's follow the numbers in the diamonds.
1. The adversary conducted a reconnaissance on Victim 1.
2. From the result of action 1 reconnaissance, the adversary conducted further recon
3. The adversary now delivers the attack to Victim 1
4. The exploit has been executed/ ran
5. Along with the exploit is a hook with the adversary's C2C server (command and control)
6. Along with the exploit is another server of the advsersary (probably a backup C2C)
7. The adversary does what it wants to do
8. From Victim 1, the adversary is able to pivot to do reconnaissance attack against Victim 2.
9. [this is a dotted diamond, referring to a hypotheses, not an actual event] the adversary went back to Victim 1 i.e. check on data perhaps
10. The adversary now delivers the attack to Victim 2
11. The adversary conducted a reconnaissance on Victim 3.
12. The adversary delivers the attack to Victim 3
13. C2C connection is established with Victim 3.
14. The adversary does what it wants to do