die Parzelle
plot of land
A delimited, surveyed piece of land that is often used as a garden or for building a house.
Sie haben eine kleine Parzelle in einer Schrebergartenkolonie gepachtet.
They leased a small plot in an allotment garden colony.

plot / parcel
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plot of land
A delimited, surveyed piece of land that is often used as a garden or for building a house.
Sie haben eine kleine Parzelle in einer Schrebergartenkolonie gepachtet.
They leased a small plot in an allotment garden colony.

The word 'Parzelle' (plot/parcel) belongs more to formal or official language, especially when referring to pieces of land and their surveying or legal division.
Im Grundbuch ist jede Parzelle mit einer eigenen Nummer verzeichnet.
In the land register, each parcel is recorded with its own number.
The context tells you whether a piece of land or an abstract section is meant. If it is about a garden plot or building land, the first meaning is intended. If it is about dividing an area for an experiment, the second meaning is intended.
Er baut Gemüse auf seiner kleinen Parzelle an.
He grows vegetables on his small plot.
In connection with plots of land, 'Parzelle' (plot/parcel) is often used with verbs such as 'pachten' (to lease), 'kaufen' (to buy), 'verkaufen' (to sell), or 'bebauen' (to build on).
Die Familie möchte eine Parzelle am See pachten.
The family would like to lease a plot by the lake.
When referring to the division of a larger area, 'Parzelle' (plot/section) is often used in the plural with the verbs 'einteilen' (to divide) or 'unterteilen' (to subdivide). The preposition used is 'in' with the accusative.
Der Acker wurde für den Versuch in zwanzig gleich große Parzellen eingeteilt.
The field was divided into twenty equally sized plots for the trial.
area / surface
'die Fläche' and 'die Parzelle' can both mean a piece of ground or land. However, 'die Fläche' is more general. It describes an area, for example on the ground, in a park, or in the landscape. 'die Parzelle' is more specific: it is a clearly delimited and often surveyed plot of land, for example in an allotment garden association or on a building plot. Learners may confuse the words because both refer to land or space. If only the size or the area is important, 'Fläche' fits. If it is about an individual, clearly delimited plot of land, 'Parzelle' is more precise.

Die kleine Parzelle am Rand der Stadt wird als Garten genutzt.
The small plot of land on the edge of the city is used as a garden.
Wir haben die nasse Fläche im Park zur Sicherheit abgesperrt.
We cordoned off the wet area in the park for safety.