1. 落后；赶不上
    If one thing or person lags behind another thing or person, their progress is slower than that of the other.

    e.g. Britain still lags behind most of Europe in its provisions for women who want time off to have babies...
           英国在妇女生育福利方面依然落后于欧洲大多数国家。
    e.g. The restructuring of the pattern of consumption in Britain also lagged behind...
           在消费结构重组方面，英国也落后于人。

2. 间隔；间歇；时间差
    A time lag or a lag of a particular length of time is a period of time between one event and another related event.

    e.g. There's a time lag between infection with HIV and developing AIDS...
           从感染艾滋病病毒到病发有一段滞后期。
    e.g. Price rises have matched rises in the money supply with a lag of two or three months.
           在增加货币供应两三个月后，物价也跟着上涨。

3. 给（屋顶、水管或水箱）装绝热层
    If you lag the inside of a roof, a pipe, or a water tank, you cover it with a special material in order to prevent heat escaping from it or to prevent it from freezing.

    e.g. If you have to take the floorboards up, take the opportunity to lag any pipes at the same time...
           如果一定要把地板掀开，不妨趁此机会给各个管道加一层隔热保护。
    e.g. Water tanks should be well lagged and the roof well insulated.
           水箱和屋顶都需要敷设严密的保温层。