This will be 101 for most scientists/mathematicians, but I’ve noticed that amongst computing students there isn’t a known difference between the two. So here it is, a quick a break down of what they are, it’s extremely easy to understand, the reason you don’t already is simply because nobody ever explained it to you.
Pi = 3.14159265359
This is the measure of how close the measured value is to the actual value. So an accurate representation of pi (written above) would be 451.9874215645123. This is more accurate than the value written above but is much less precise.
This is the measure of how close measured values are to each other. So 3 is more precise than the previous example as it is closer to pi, but it is much less precise.