What to call value compared with the previous day's value in stock exchange?

It is called daily percentage change :

The example below refers to currencies but the same apply to stocks:

• the change of currency rate related to the previous daily close and displayed in percentage points.

Percentage Change:

• Percentage change is a simple mathematical concept that represents the degree of change over time. It is used for many purposes in finance, often to represent the price change of a security.

BREAKING DOWN 'Percentage Change':

• Percentage change can be applied to any quantity that you measure over time. Let's say you are tracking the quoted price of a security. If the price increased, use the formula [(New Price - Old Price)/Old Price] and then multiply that number by 100. If the price decreased, use the formula [(Old Price - New Price)/Old Price] and multiply that number by 100.

(Investopedia)

Those are daily percentage changes, which is a common way to report relative change. The other numbers are the actual daily change.

For more details, see the Wikipedia article on "relative change”.

The linked article is long, but the basic idea is stated as

"In any quantitative science, the ... [term] relative change ... [is] used to compare two quantities while taking into account the "sizes" of the things being compared. The comparison is expressed as a ratio and is a unitless number. By multiplying these ratios by 100 they can be expressed as percentages so the terms percentage change, percent(age) difference, or relative percentage difference are also commonly used." In my personal experience, "percentage change" is by far the most common.