Removing a trend from time series data

What is a time series and what is a trend in a time series dataset? If there’s a trend in a series, how can we remove it and why would we want to remove it? Given this dataset, remove the trend from the series.

To help get you started, below is code (Python) to import the referenced dataset:

# Import libraries
%matplotlib inline
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
# Import data
df = pd.read_csv('https://raw.githubusercontent.com/erood/interviewqs.com_code_snippets/master/Datasets/timeseries_v1.csv')