Your card is authorized during Checkout, but not charged until the day your order is received.
Due to possible variances in item weights and substituted products, your final order amount is not known until your order has been hand picked at the store. To account for this your card is authorized, but not charged, during the Checkout process. The authorized amount is equal to your estimated total, which is displayed in the Order Details section during Checkout (example below). This appears as a pending transaction on your card's statement.
When the store finishes preparing your order, these variable weights and substitutions are finalized, and your card will then be charged for the exact amount of products you actually receive. The final charge on your card will occur on the day that you are to pick up or receive your groceries, but the authorization will appear on your account on the day that you place your order. If the final total is greater than your estimated total, the order difference will appear as a second transaction on your statement.