Hi, word cloud is a way of visualizing frequency of words, or during sentiment analysis,etc.
Below image is an example of word cloud.

I'm taking superstore as data source. lets see how word cloud id built in tableau. (Tableau allows only horizontal and vertical font for word clouds)
Consider the visualization that shows the sum over profit over different sub categories using word cloud.
Select sales,profit and category then click on packed bubbles chart from show me panel.

Then click on text view from marks pane and select text.

Another example,

This is a simple word cloud.
hope this helps you.