jiffies
also: kernel ticks, timer ticks
Jiffies are the smallest unit of kernel time in Linux, representing the time between timer interrupts. The kernel uses jiffies to track elapsed time and schedule processes.
Jiffies are internal kernel ticks that measure time at the lowest granularity. Each jiffy represents one timer interrupt interval, typically 1/100th to 1/1000th of a second depending on your kernel's CONFIG_HZ setting. The kernel increments a global jiffies counter with every timer tick.
The kernel uses jiffies to implement timeouts, process scheduling, and periodic tasks. For example, when you call sleep(1), the kernel calculates the target jiffies value and puts your process to sleep until the counter reaches it.
You can inspect jiffies-related values in /proc/uptime (in jiffies) and check the current jiffy value in kernel code. A higher CONFIG_HZ value means smaller jiffy intervals but more frequent timer interrupts.