Some terms

There are some terms you need to know when you conduct research and write a thesis. Here they are.

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A concept is a word that refers to an object or an event.
Example: book, table, jump, slow, loud, shiver.
You can perceive them using your senses. You can see a book or a table, you can see someone jump, you can see a slow thing, you can hear something loud, etc.

A construct is a psychological concept.
Example: motivation, intelligence, reading ability, language acquisition.
You cannot perceive them using your senses because they are 'psychological'. Even if you open someone's head, you cannot see their intelligence, motivation, or reading ability. But they exist!

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Constitutive definition: a word is defined by using other words.
Example:
A student is a person studying in a school or a university.
Conference proceedings can be defined as a collection of scientific papers presented in a conference.

Operational definition: a word is defined by mentioning the operation that must be done to measure the concept/construct.
Example:
Intelligence quotient is defined as the scores on the Stanford-Binet Test of Intelligence.
English proficiency is defined as the scores of Test of English as a Foreign Language (TOEFL).

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A variable is something that varies.
Example:
Age can be 12 years old, 38 years old, 50 years old, etc. Age varies so it is a variable.
Gender can male or female. Gender varies so it is a variable.
English proficiency can be good, average or poor. English proficiency varies so it is a variable.