Development is another word for betterment or alleviation of a concept, society or whatever is the reference in which it is used.
When the word development is used as a stand-alone word, it usually refers to the economy or the society. The commonly understood criteria for development are:
Per capita income
The income level per person in a society is a rough indicator of the buying capacity of the society. A good level of income ensures that the people have access to basic requirements of food clothing and shelter. To be understood completely however, the per capita income needs to be adjusted to the cost of living, and to the differences in currencies to be compared globally. Also since this is just an average it is subject to extremes.
Basic needs and infrastructure
The basic needs like food, housing and potable water needs to be available for the masses. Other infrastructure facilities like electricity, roads etc. have to be made available for a society at a basic level.
When every citizen is educated, it is a sign of development. All the supporting infrastructure needs to be made available.
After this basic level of needs is met, any addition, such as better transport system, industrialisation, better security, banking infrastructure, legal infrastructure, institutes for higher education etc. makes the economy better and more developed.