This is the 47th most frequent Catalan word.
gran
Big; large; great; old (in age).
In this sentence, 'gran' describes size, meaning 'big' or 'large'.
Aquella biblioteca és molt gran.
That library is very big.
'Gran' here conveys a sense of greatness or noteworthy quality, indicating generosity.
Té un gran cor per ajudar els altres.
They have a great heart for helping others.
Here, 'gran' is used to indicate advanced age.