Social Slots allow you to change the cosmetic looks of your armor, but still keep the statistics of your original armor. If you click on the top picture you'll see the Jungle Armor equipped, but it's showing the Shadow Armor that are in the Social Slots. If you are wearing a full set of Molten Armor and put on clothing or armor, light is no longer produced when walking, because the special effect of your Social Slot armor will be shown. For the record, Molten or Meteorite Armor's light will be produced if you have the full set in your Social Slots.

Terraria - Social Slots(00:28)
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If you are in Multiplayer and have an armor set equipped (with social gear over them), if you enable PVP the social gear will disappear and only the equipped armor will show.

If you don't care about looks, you can always use the social slots as storage for an alternate set of armor. Easily swapping between your energy set and your close combat set (or whatever sets you use) without taking up precious inventory space. A player can do this by right clicking the corresponding social slot.

Outfits:

• Hero Outfit
• Tuxedo
• Ninja Outfit
• Familiar Outfit
• Archaeologist's Outfit
• The Doctor's Outfit
• Plumber's Outfit

Other:

• Bunny Hood
• Gold Crown
• Mime Mask
• Red Hat
• Robe