The proximal contact points or the area refers to the surface point or area where the proximal surfaces of neighboring teeth come in contact. Contact point/area is usually found in the occlusal one third of the natural crown of most of the teeth.
It creates a natural embrasure supplying an opportunity for the good maintenance of the hygiene of the inter-proximal area.
An ideal contact supports the dental arch stability by transmitting the forces along the long axis of the teeth.
Ideal proximal contact acts as a barrier against food impaction and thus contributes to the underlying periodontal health by providing spillway for food and easing hygienic cleaning.
The correct relationship with the adjacent tooth allows a good support to the teeth against masticatory forces and promotes the deflection of the food through the embrasure.
The correct contact areas help in proper speech and esthetics, especially in the anterior region.
Faulty contacts lead to restorative defects which hamper the health of the periodontium.
Too broad contact bucco-lingually or occlusal-gingivally causes change in the tooth anatomy, improper shunting of food in bucco-lingual direction because of narrow embrasure. This condition leads to food impingement in the contact area and contact area which is more concave or flat. These conditions also result in improper physiological movement of the tooth.
Too narrow contact bucco-lingually or occluso-gingivally causes wide embrassures. This situation leads to greater food retention and plaque accumulation.
Contact area placed too occlusally, buccally or lingually will result in flattened marginal ridge of the restoration,
Contact points too gingivally will lead to increased depth of occlusal embrasure, and loose contact creates continuity between embrasures leading to food impaction.
It is common to see good proximal contact but inadequate contour in proximal restoration. Similarly, a good contour with the poor proximal contact can be possible.
It is to be noted that establishing the correct inter-proximal contact is the primary aim of restorative procedures, besides restoring the missing part of the tooth and its function.
Relative position of contact points (black lines) in maxillary and mandibular teeth 
Contact point in maxillary posterior teeth being seen from occlusal view showing their relative position buccolingually (see the dots)
Ref:
________________