Visa shopping is the practice of applying for a visa from the country where it is faster or easier to get as compared to others.
As per Schengen Visa main rule, if you are travelling to more than one country, you should apply for a visa from the country with the maximum stay.
In the case, you plan to visit two or more countries for an equal number of days (we are talking few days of difference), then you should apply for a visa from the country that you visit first or is your main destination.
However, many people do not abide by the Schengen visa rules. They tend to apply for visas at Embassies, which are easier or faster to get. Then they use that visa to stay in other countries for a longer period.
Be aware, Embassies are doing very thorough check of the travel plans.
Also there might be more severe consequences – starting with the refusal of the visa and if travelling with different itinerary, ending up to be offloaded from the plane or returned back home from the EU borders.
ALWAYS APPLY FOR A VISA FROM THE COUNTRY YOU PLAN TO VISIT!