How to create Taxonomy Term using Services?
I'm using POSTER plugin (for Firefox) to post data. 

Here are the parameters.

URL: [your path]/[end-point]/taxonomy_term.json

Content Type: application/json

Actions: POST

Here are the JSON formats.

To create Taxonomy Term

{
    "vid": "1",
    "name": "My First Tag",
    "description": "Term description",
    "vocabulary_machine_name": "tags"
}


To update Taxonomy Term

{
    "tid": "14",
    "vid": "1",
    "name": "My First Tag Edit",
    "description": "Term description changed"
}


Here tid is taxonomy id and vid is vocabulary id of the Taxonomy.

Hope it helps someone.