what is the difference between neotype and syntype?????

These are the codes of nomenclature by
International Code of Zoological Nomenclature
and
International Code of Botanical Nomenclature:
Before giving you meaning Syn= same; Neo = new.
Just remember this and read the belwo eaning of them.

Syntype:
A syntype is any specimen mentioned in the catalogue
when no organism is designated,
or any one of two or more specimens simultaneously designated as types.

Neotype:
When a holotype or a previously designated organism has been lost or destroyed
and it can be shown that all the other original material differs
destroyed type,
a neotype may be selected to preserve the usage established by the previous typification