What is the lever on the left side slide that disengages the firing mechanism called?

The lever on the left side slide that disengages the firing mechanism is commonly referred to as the safety/de-cocking lever. This component serves a dual purpose: it acts as a safety mechanism to prevent the firearm from discharging unintentionally and as a de-cocking feature to safely lower the hammer when the firearm is de-cocked.

When the safety/de-cocking lever is engaged, it typically inhibits the trigger from being pulled, thus preventing accidental discharges. Additionally, when utilized for de-cocking, it allows the user to lower the hammer safely without firing a round. This lever is essential for enhancing the safety of the firearm during handling and storage, particularly in situations where the firearm is not immediately needed for operational use.

Understanding the functionality of this lever is critical for safe firearm handling practices and is a key component that is taught in peace officer training to ensure the safe use of firearms.