liegend
lying
Describes the state of being in a horizontal position, that is, not standing or sitting.
Der Patient muss nach der Operation mehrere Tage liegend verbringen.
After the operation, the patient must spend several days lying down.

lying
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lying
Describes the state of being in a horizontal position, that is, not standing or sitting.
Der Patient muss nach der Operation mehrere Tage liegend verbringen.
After the operation, the patient must spend several days lying down.

'Liegend' (lying) is the present participle of the verb 'liegen' (to lie). It describes an ongoing state and is used like an adjective.
Auf dem Sofa lag eine schlafende Katze.
A sleeping cat was lying on the sofa.
'Liegend' can stand before a noun or describe a verb. It answers the question 'Wie?' (how?).
Der liegende Baum blockierte die Straße.
The fallen tree blocked the road.
The word is often used in instructions and notices for transport or storage. It means that an object must not stand upright.
Bitte transportieren Sie den Kühlschrank nicht liegend.
Please do not transport the refrigerator lying down.
standing
'stehend' and 'liegend' both describe the position of people or things. Here, they are opposites. 'stehend' means upright and vertical, so not sitting or lying down. 'liegend' means horizontal, for example on the bed, on the floor, or on the table. They can be confusing because both are often used as participles like adjectives. Pay attention to the direction: upward is 'stehend', flat on a surface is 'liegend'.

Die liegende Katze schläft ruhig auf dem Sofa.
The lying cat is sleeping peacefully on the sofa.
Wegen des vollen Busses fährt Paul stehend zur Arbeit.
Because the bus is full, Paul rides to work standing.