POST query parameters are sent by HTTP clients for example by forms, or when performing a POST request sending data.

How can you access this data?

If the data was sent as JSON, using Content-Type: application/json, you will use the express.json() middleware:

const express = require('express')
const app = express()

app.use(express.json())

If the data was sent using Content-Type: application/x-www-form-urlencoded, you will use the express.urlencoded() middleware:

const express = require('express')
const app = express()

app.use(express.urlencoded())

In both cases you can access the data by referencing it from Request.body:

app.post('/form', (req, res) => {
  const name = req.body.name
})

Note: older Express versions required the use of the body-parser module to process POST data. This is no longer the case as of Express 4.16 (released in September 2017) and later versions.