Close down an airport or other facility due to thick fog or other weather conditions impeding visibility, as in The airport was socked in all morning and air traffic was at a standstill, or We finally got to the peak and were totally socked in—there was no view at all. The sock referred to here is probably a windsock, as decisions to close an airport are made in part on the basis of observations of wind-socks, which indicate wind direction. The expression was first recorded in 1944.