You can name it as you want it's just the object of the "foreach" qweb loop. It's normally at the top of the template.

<template id="report_my_report">
    <t t-call="report.html_container">
         <t t-foreach="docs" t-as="o">

The docs is what you pass to the template. 

In QWEB, o is an instance of active model(it can sale.order,purchase.order,account.invoice...etc), and it contains each value of the model you want to print

For example you have an object (res.partner(1)) . Than by using your code you can get records from that object using alias "o".

o.name

o.gender

etc