CLK - Clock

RTC - Realtime Clock

MCO - Microcontroller Clock Output

WDG - Watchdog

HRTIM - High-resolution Timer

IWDG - Independent Watchdog

RC - Oscillator made with an RC (resistor-capacitor) circuit

CSS - Clock Security System

LSI, LSE - Low speed clock

HSI, HSE - High speed clock

PLL - Phase-locked loop (clock with same phase as its input?)

Mux - Multiplexer

APB# - Advanced Peripheral Bus

AHB# - Advanced High-performance Bus

HCLK - Internal AHB Clock

PCLK - Internal APB clock

FCLK - AHB clock that doen’t go to sleep when the CPU goes to sleep. Can wake up the CPU during inturrupt