What do you mean by ortho and para directing groups? Explain the ortho and para directing effect by taking the example of any group.

(N/A) Definition: In a monosubstituted benzene,if an incoming electrophile attacks the ortho and para positions with respect to the first substituent group $(Z)$,then the first group $(Z)$ is called an ortho and para directing group.
Examples: $-OH, -OCH_3, -NH_2, -CH_3, -C_2H_5, -NHCH_3, -NHR, -NHCOCH_3, -NHCOR$ etc.,are ortho and para directing groups.
$(b)$ Explanation of the directing properties of the $-OH$ group: The $-OH$ group (hydroxyl group) is ortho and para directing. This can be explained by the resonance structures of phenol,as shown below:
[Resonance structures of phenol showing increased electron density at ortho and para positions]
Due to the $+R$ effect of the $-OH$ group,the electron density increases at the ortho and para positions of the benzene ring. Consequently,an electrophile $(E^+)$ is more likely to attack these electron-rich positions,leading to ortho and para substitution products.