What is the meaning of lagging?

noun

• Used to wrap around pipes or boilers or laid in attics to prevent loss of heat.

verb

• Hang (back) or fall (behind. in movement, progress, development, etc.)
  • synonyms: lag, dawdle, fall back, fall behind
• Lock up or confine, in or as in a jail.
  • usage: "The suspects were imprisoned without trial"; "the murderer was incarcerated for the rest of his life"
  • synonyms: imprison, incarcerate, lag, immure, put behind bars, jail, jug, gaol, put away, remand
• Throw or pitch at a mark, as with coins.
  • synonyms: lag
• Cover with lagging to prevent heat loss.
  • usage: "lag pipes"
  • synonyms: lag