What is the meaning of δ?

A (path-dependent, inexact) differential.

A small number, usually accompanied by ε.

Kronecker delta or Dirac delta.

a voiced dental plosive (IPA [d̪]).

a voiced dental fricative (IPA ð).

declination

The 6th letter of the Arvanitic Albanian Greek-script alphabet.

Lower case delta (δέλτα), the fourth letter of Greek alphabet. It represented in Ancient Greek a voiced dental plosive: /d/ and in modern Greek a voiced dental fricative: /ð/. It is preceded by γ and followed by ε.

A letter of the Cypriot Arabic alphabet, written in the Latin script.

A letter of the Wakhi alphabet, written in the Latin script.

Lower case delta (δέλτα), the fourth letter of Greek alphabet. It represents in modern Greek a voiced dental fricative: /ð/. It is preceded by γ and followed by ε.

Abbreviation of δεσποινίς (despoinís): Miss

Source: wiktionary.org