sixteenth rest, quarter rest, half rest, whole rest

Whole rest. An easy way to remember which rest is which is that a whole rest looks like a hole, and a half rest looks like a hat.

sixteenth rest, quarter rest, half rest, whole rest

Both are held for the full duration of a measure. A whole note is played for an entire measure, and a whole rest means the instrument is silent for an entire measure.

Not just in orchestra, but in all music, a whole rest indicates that no notes are played for an entire measure.