A meniscus is the curve in the surface of a liquid contained within a (usually narrow) container, such as a graduated cylinder. Take a look at the graphic to the right.

The numerical value we read for the volume of liquid contained in this cylinder will depend on what part of the meniscus we choose to look at. Graduated cylinders and other containers are calibrated such that we should get the most accurate reading by looking at the center of the meniscus from eye level. If we don’t look at the meniscus from eye level, something called parallax error will occur that will distort our perception of level of the meniscus.