What is bandwidth? And how to measure it?

Bandwidth is the width or space that is available for transmission of the amount of data through it

$The \quad range \quad of\quad frequencies \quad a\quad channel\quad can\quad pass\begin{cases} 100Hz & \text{}\\ 400Hz & \text{}\\ 600Hz & \text{}\\ 800Hz & \text{} \end{cases}$ $Bandwidth(bw)=Highest frequency(f_h)- Lowest frequency (f_l)$

Narrowband: means its bandwidth $(f_h-f_l)$ is much smaller ( by a factor of 10 or more) when compared with median frequency $(f_h+f_l)/2$ otherwise it is called a Wideband

Bandlimited: the signal is bandlimited when its spectrum is zero outside its frequency range

$|f| \geq Bw$

An analogy to understand bandwidth

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Consider road as a channel, and vehicles as data the wider the road the more vehicle can pass through it

The same analogy applies to bandwidth the wider the bandwidth the larger the amount of data can be transferred or pass through it, the narrower the BW more congested will the channel and data congestion will lead to network slow down