Points or lines are said to be **coplanar** if they lie in the same plane.

**Example 1:**

The points $P$, $Q$, and $R$ lie in the same plane $A$.

They are *coplanar*.

**Example 2:**

The points $P$, $Q$ and $R$ lie in the plane $A$ and the point $S$ lies on the plane $B$.

They are *non coplanar*.

**Example 3:**

The two lines $\overleftrightarrow{PQ}$ and $\overleftrightarrow{RS}$ lie in the same plane $A$.

They are *coplanar*.

**Example 4:**

The two lines $\overleftrightarrow{PQ}$ and $\overleftrightarrow{UV}$ are skew lines.

They are *non coplanar*.