Moneyness locates a strike relative to the stock: in the money (intrinsic value now), at the money (strike near spot), out of the money (all time value). Almost every options property (delta, gamma, decay, assignment odds) organizes along this axis.
At the money is where gamma and time decay peak and where delta sits near 0.50. Deep in the money behaves like stock; far out of the money behaves like a lottery ticket. Premium-selling disciplines live in the out-of-the-money band (short strikes at 0.15-0.30 delta), while stock-replacement positions live in the money around 0.70-0.75 delta; the band is the strategy.