The Cyber Kill Chain model is one of the models that's used to represent the phases that an attack moves through to obtain their objective. The phases, derived from the Lockheed Martin and military models, are reconnaissance, weaponization, delivery, exploitation, installation, command and control (C2), and actions on objectives.
Reconnaissance is about information gathering. This might be about the system in general, but is more likely to be targeted at areas with known vulnerabilities. This can reveal information about the attacker or groups that are involved.
Weaponization is where the attacker links the information that's gathered during reconnaissance with known vulnerabilities and exploits.
The delivery phase aims to get the tools to the right location to enact the exploit. This is often an email or a physical delivery (for example, a USB drop).
Exploitation...