1. Focus of conic. See [ellipse] and [parabola]

2. The intersection of reflected or refracted light parallel to the main axis of a spherical mirror or lens on the main axis. A spherical mirror has a focal point; The lens has two focal points, one on each side of the lens.

3. Metaphor is the key to the problem or the focus of debate, or the focus of people's attention.

Hu Shi? Sinology Quarterly published a declaration: "Everyone's eyes and efforts are focused on a few Confucian classics." ?

Mao Dun? "Midnight" IX: "Assess the weight of his every word, and at the same time, I feel that the current negotiations are very difficult. Zhao's insistence is the focus of Wu Sunfu's refusal to give in. "

Synonyms: theme, center and core

Extended data:

Synonym definition:

First, the main idea? [ zhǔ zhǐ ]

Main meaning, intention or purpose: the article is unclear.

Xia Mianzun Ye Shengtao? Wen Xin VI: "The main idea is that young people should know justice, imperialism and themselves.

Lu Xun? "Three Leisure Collection of Bell Tower": "Sometimes when I see an acquaintance around me, I entrust him, ask him to read it and tell me the general idea of the letter." ?

Second, the center? [zh ng xn]

1. Equal distance from the surroundings: there is an octagonal pavilion on the grass.

2. The main part of things: ~ thoughts. ~ question. ~ work.

3. Cities or regions that occupy an important position in one aspect: politics. Culture.

4. Institutions and units with relatively complete equipment and technical strength (mostly unit names): maintenance ~. Study ~. Scientific and technological information ~.

Mao Zedong's On the Coalition Government: "Yan 'an is the guiding center of all liberated areas. "

People's Daily 1983-8-3: "Beijing is the capital of our great socialist motherland and the political and cultural center of the whole country."

Third, the core? [héxén]

Center; The main part (on the relationship between things): leadership ~. ~ group. ~ fortification. ~ action.

Mao Zedong: "China's * * * production party is the core of the leadership of the people of China. Without such a core, the socialist cause cannot be won. " (Excerpted from Mao Zedong's Collected Works, Volume VII, page 303, with the original title "China * * * Production Party is the leading core of the people of the whole country", this is Mao Zedong's speech when the central leaders of China * * * received all the delegates of the Third National Congress of China New Democratic Youth League, People's Publishing House, 1999 edition).