What is the meaning of underlay?

noun

• A pad placed under a carpet.
  • synonyms: carpet pad, rug pad, underlayment

verb

• Raise or support (the level of printing) by inserting a piece of paper or cardboard under the type.
  • usage: "underlay the plate"
• Put (something) under or beneath.
  • usage: "They underlaid the shingles with roofing paper"
• Provide with a base, support, lining, or backing.
  • usage: "underlay the boards with joists"
• Be or form the base for.
  • synonyms: underlie
• Lie underneath.
  • synonyms: underlie