Nasalization
Consider this word.
हिन्दी hindī
This same word, may also be written as shown below, with no change in pronunciation. The difference below is that the ‘n’ consonant is replaced by a ‘bindu,’ or dot, above the line.
हिंदी hindī
Both of these spellings are correct. The bindu indicates that the vowel sound under it is nasalized. Sometimes you may see a chandrabindu is used instead of a bindu.
हाँ hān
Here are some more examples.
लम्बा lambā
अण्डा anḍā