Brendan Gregg

$ uptime
 16:48:24 up  4:11,  1 user,  load average: 25.25, 23.40, 23.46

top - 16:48:42 up  4:12,  1 user,  load average: 25.25, 23.14, 23.37

$ cat /proc/loadavg 
25.72 23.19 23.35 42/3411 43603

Some interpretations:

• If the averages are 0.0, then your system is idle.
• If the 1 minute average is higher than the 5 or 15 minute averages, then load is increasing.
• If the 1 minute average is lower than the 5 or 15 minute averages, then load is decreasing.
• If they are higher than your CPU count, then you might have a performance problem (it depends).

wikipedia

An idle computer has a load number of 0 (the idle process isn’t counted). Each process using or waiting for CPU (the ready queue or run queue) increments the load number by 1. Each process that terminates decrements it by 1. Most UNIX systems count only processes in the running (on CPU) or runnable (waiting for CPU) states. However, Linux also includes processes in uninterruptible sleep states (usually waiting for disk activity), which can lead to markedly different results if many processes remain blocked in I/O due to a busy or stalled I/O system.[1] This, for example, includes processes blocking due to an NFS server failure or too slow media (e.g., USB 1.x storage devices). Such circumstances can result in an elevated load average which does not reflect an actual increase in CPU use (but still gives an idea of how long users have to wait).

Multicore / multiprocessor

On multi-processor system, the load is relative to the number of processor cores available. The “100% utilization” mark is 1.00 on a single-core system, 2.00, on a dual-core, 4.00 on a quad-core, etc.

For the purposes of sizing up the CPU load value, the total number of cores is what matters, regardless of how many physical processors those cores are spread across.