The word lord in English has several related meanings.
The original meaning is ‘master’ or ‘ruler’ and in this sense it is often used to refer to human beings: ‘the lord of the mansion’ or ‘Lord So-and-So’ (in the United Kingdom, for example).
The word Lord with a capital L is used in the lexicon of Islam to
refer to the One and Only God – Allah. In Islam, there is no
ambiguity about the meaning of this word. While it is true that
one may occasionally use the word lord (whether capitalized or
not) to refer to a human being, in Islamic discourse the
reference of this term is always clear from the context. Whereas
for Christians, Hindus and other polytheists, the word Lord with
a capital L may refer to Allah, to Jesus or to some imagined
deity, for Muslims, there can be no plurality of meaning. Allah
alone is the Lord, and the Lord is Allah – not Jesus, not Rama,
not any other being.