die Großmutter
grandmother
The mother of one's own father (paternal grandmother) or one's own mother (maternal grandmother).
Jeden Sonntag besuchen wir meine Großmutter zum Kaffeetrinken.
Every Sunday we visit my grandmother for coffee.

grandmother
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grandmother
The mother of one's own father (paternal grandmother) or one's own mother (maternal grandmother).
Jeden Sonntag besuchen wir meine Großmutter zum Kaffeetrinken.
Every Sunday we visit my grandmother for coffee.

The word is made up of 'groß' (big/great) and 'Mutter' (mother). The prefix 'Groß-' is used with family members to refer to one generation earlier, similar to 'grand-' in English.
Meine Urgroßmutter wurde 99 Jahre alt.
My great-grandmother lived to be 99 years old.
Other relatives of this generation are named according to the same pattern. The male counterpart is 'der Großvater' (grandfather), and together they are 'die Großeltern' (grandparents).
Meine Großeltern leben auf dem Land.
My grandparents live in the countryside.
'Großmutter' (grandmother) is the neutral and also somewhat more formal expression. It is often used in written language or when talking about one's family in a more official context.
In ihrem Testament hat die Großmutter das Haus den Kindern vermacht.
In her will, the grandmother left the house to the children.
grandma
'Oma' and 'Großmutter' can both mean the mother of your own mother or father. 'Oma' is colloquial, personal, and often affectionate. 'Großmutter' sounds more neutral and somewhat more formal, for example in texts, forms, or when speaking in a factual way. Learners may confuse the words because in a family they often refer to the same person. The important point is style: at home, people usually say 'Oma'; in official or factual situations, 'Großmutter' is more likely. 'Oma' can also mean an older woman in general, but that is very colloquial.

Für den Stammbaum schreibt Lisa den Namen ihrer Großmutter auf.
For the family tree, Lisa writes down her grandmother's name.
Am Sonntag backt meine Oma immer einen Kuchen.
On Sundays, my grandma always bakes a cake.