What is the term for a word or phrase that is spelled the same backward as forward?

Palindrome (noun): 
English Meaning - A word or group of words that is the same when you read it forward from the beginning or backward from the end. 
Bangla Meaning - যে শব্দ, কবিতার চরণ ইত্যাদি উল্টা দিক থেকে পড়লেও একই থাকে।
Example - "Refer" and "level" are palindromes.

Other options, 
Anagram - A word or phrase made by using the letters of another word or phrase in a different order. "Neat" is an anagram of "a net".
Homonym - A word that sounds the same or is spelled the same as another word but has a different meaning. "No" and "know" are homonyms.
Synonym - A word or phrase that has the same or nearly the same meaning as another word or phrase in the same language. The words "small" and "little" are synonyms.

Source: 
1. Cambridge Dictionary. 
2. Accessible Dictionary by Bangla Academy.