These are important aspects of all electronic components, particularly resistors and capacitors.
The tolerance on the value of a component is a measure of how accurate its value is. For example, a resistor of nominal value l0,000Ω , and a tolerance of±10%, may have an actual resistance between 9,000Ω (ie 10,000- l0%)and 11,000Ω (ie 10,000+ 10%). The usual tolerances on the values of resistors and capacitors are ±20, ±10, ±5, ±2 and ±1%.
Generally the value of a component increases as the temperature increases. A constant known as the 'temperature coefficient' is a measure of this increase, and thus (for most items) the temperature coefficient is positive.
There are a few exceptions, eg ceramic capacitors having a negative temperature coefficient can be made. Carbon and semiconductors have a negative coefficient.